Nickel manganese composite hydroxide and method for producing same, positive electrode active material for nonaqueous electrolyte secondary battery and method for producing same, and nonaqueous electrolyte secondary battery

ABSTRACT

Provided are a nickel-manganese composite hydroxide capable of producing a secondary battery having a high particle fillability and excellent battery characteristics when used as a precursor of a positive electrode active material and a method for producing the same. A nickel-manganese composite hydroxide is represented by General Formula: Ni x Mn y M z (OH) 2+α  and contains a secondary particle formed of a plurality of flocculated primary particles. The primary particles have an aspect ratio of at least 3, and at least some of the primary particles are disposed radially from a central part of the secondary particle toward an outer circumference thereof. The secondary particle has a ratio I(101)/I(001) of a diffraction peak intensity I(101) of a 101 plane to a peak intensity I(001) of a 001 plane, measured by an X-ray diffraction measurement, of up to 0.15.

TECHNICAL FIELD

The present invention relates to a nickel-manganese composite hydroxideand a method for producing the same, a positive electrode activematerial for a nonaqueous electrolyte secondary battery and a method forproducing the same, and a nonaqueous electrolyte secondary battery.

BACKGROUND ART

With the recent wide spreading use of portable electronic devices suchas a mobile phone and a notebook personal computer, there has been astrong demand to develop a small and light nonaqueous electrolytesecondary battery having a high energy density. As the nonaqueouselectrolyte secondary battery like this, a lithium ion secondary batterymay be cited. In the negative electrode material of the lithium ionsecondary battery, a lithium metal, a lithium alloy, a metal oxide, acarbon, or the like is used. These materials can de-insert and insertlithium.

The lithium ion secondary battery like this is now under active researchand development. Among them, the lithium ion secondary battery using, inthe positive electrode thereof, a lithium-transition metal compositeoxide, especially a lithium-cobalt composite oxide (LiCoO₂) that iscomparatively easily synthesized, can generate a high voltage of a 4-Vclass; and thus, this is hoped as the battery having a high energydensity; and it is being put in actual use. Also, a lithium-nickelcomposite oxide (LiNiO₂), a lithium-nickel-cobalt-manganese compositeoxide (LiNi_(0.33)Co_(0.33)Mn_(0.33)O₂), and the like using nickel,which is cheaper than cobalt, have been developed. Among them, thelithium-nickel-cobalt-manganese composite oxide is drawing attentionbecause this is comparatively cheap and has an excellent balance amongheat stability, durability, and so forth. However, because the capacitythereof is inferior to that of a nickel type, enhancement of thecapacity (energy density) is demanded. In addition, for the lithium ionsecondary battery, not only the battery capacity but also excellentoutput characteristic and cycle characteristic are demanded.

In order to enhance the capacity, it is important to enhance not onlythe capacity per a unit weight of the active material but also theenergy density per a unit volume thereof. In order to enhance thecapacity per a unit weight of the active material, for example, inPatent Literature 1, the active material having a narrow particle sizedistribution with a uniform particle diameter is proposed. Because theactive material like this can undergo a uniform electrochemicalreaction, it has characteristics of a high capacity and a long life; onthe other hand, because there is a tendency of a poor particlefillability, it cannot say that the volume energy density thereof ishigh.

As the study about the method to enhance the capacity per a unit weightin an alternative way, control of a particle structure may be cited. Forexample, Patent Literature 2 indicates that when a precursor hydroxideis lightly crushed followed by granulation and spheroidization so as toinclude voids therein, a positive electrode active material having ahigh ratio of an open pore can be obtained. However, because this methodincludes a crushing process of the precursor and the subsequent processto make the slurry thereof, this is not industrial, and thus, notsuitable for mass production.

In order to enhance the energy density per a unit volume, a method isstudied how to enhance a particle fillability. For example, in PatentLiterature 3, a method in which particles having different particlediameters are mixed is proposed. Particles having larger particlediameters are separated from particles having smaller particlediameters; and by changing the weight ratio in mixing them, a positiveelectrode active material having a good fillability and competitivelysatisfying excellent rate characteristic and capacity can be obtained.However, in this method, additional processes such as the process toprepare two kinds of particles having different particle diameters arenecessary; and thus, the production cost thereof is high.

As described above, at the present time neither a lithium-metalcomposite oxide capable of satisfactorily raising the performance of thelithium ion battery nor a composite hydroxide that can be a raw materialof the composite oxide like this is developed. Furthermore, althoughmany methods for producing the composite hydroxide have been alsostudied, at the present time a method capable of producing, in anindustrial scale, the composite hydroxide that can be a raw material ofthe lithium-metal composite oxide capable of satisfactorily raising theperformance of the lithium ion secondary battery has not been developedyet. With the background like this, development of a positive electrodeactive material having a high capacity and a good particle fillabilityis wanted; and also, development of an industrially advantageousproduction method capable of realizing mass production with a reducedproduction cost is wanted.

CITATION LIST Patent Literatures

-   [Patent Literature 1] Japanese Patent Laid-Open Publication No.    2011-187419-   [Patent Literature 2] Japanese Patent Laid-Open Publication No.    2003-051311-   [Patent Literature 3] Japanese Patent Laid-Open Publication No.    2015-76397

SUMMARY OF INVENTION Technical Problems

In view of the problems described above, the present invention intendsto provide: a positive electrode active material for a nonaqueouselectrolyte secondary battery having a high battery capacity, a highoutput characteristic, and an excellent cycle characteristic withsuppressed deterioration of the battery capacity even upon repeating thecharging and discharging operations; and a nickel-manganese compositehydroxide usable as a precursor of the active material. In addition, thepresent invention provides a nonaqueous electrolyte secondary batteryhaving a high battery capacity, a high output characteristic, and a longlife because of the excellent cycle characteristic. Furthermore, thepresent invention intends to provide: a method for readily producing anickel-manganese composite hydroxide in an industrial scale; and amethod for producing a positive electrode active material for anonaqueous electrolyte secondary battery by using the nickel-manganesecomposite hydroxide.

Solution to Problems

The inventors of the present invention carried out an extensiveinvestigation about effects of the particle structure on the outputcharacteristic and the cycle characteristic of the nonaqueouselectrolyte secondary battery; and as a result, it was found that theoutput characteristic and the cycle characteristic are able to beimproved when the positive electrode active material for a nonaqueouselectrolyte secondary battery has a certain particle structure or acrystal orientation. It was also found that the particle structure ofthe positive electrode active material is significantly influenced bythe particle structure and crystallinity of a composite hydroxide thatis a precursor thereof; and thus, characteristics of the positiveelectrode active material are able to be improved by controlling theparticle structure and crystallinity of the composite hydroxide, andthat the particle structure and crystallinity of the composite hydroxideare able to be controlled by using a certain crystallization condition.The present invention has been completed based on these findings.

A first aspect of the present invention provides a nickel-manganesecomposite hydroxide, in which the nickel-manganese composite hydroxideis represented by General Formula (1): Ni_(x)Mn_(y)M_(z)(OH)_(2+α) (inFormula (1), M is at least one additional element selected from Co, Ti,V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W; and x, y, z, and α satisfy0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8,x+y+z=1.0, and 0≤α≤0.4) and contains asecondary particle formed of a plurality of flocculated primaryparticles. The primary particles have an average aspect ratio of atleast 3, and at least some of the primary particles are disposedradially in a direction from a central part of the secondary particle toan outer circumference thereof. The secondary particle has a ratio(I(101)/I(001)) of a diffraction peak intensity I(101) of a 101 plane toa peak intensity I(001) of a 001 plane, measured by an X-ray diffractionmeasurement, of up to 0.15.

Here, it is preferable that in an area within 50% of a radius of thesecondary particle from the outer circumference of the secondaryparticle toward the central part thereof, at least 50% of the primaryparticles in number relative to a total number of the primary particlespresent within this area be disposed radially. In addition, it ispreferable that a total pore volume in a pore volume distribution be atleast 0.015 cm³/g and up to 0.03 cm³/g. In addition, it is preferablethat a volume-average particle diameter MV be at least 5 μm and up to 20μm, and [(D90−D10)/average particle diameter] that is an indicator torepresent a spread of particle size distribution be at least 0.7.

A second aspect of the present invention provides a method for producinga nickel-manganese composite hydroxide, in which the nickel-manganesecomposite hydroxide is represented by General Formula (1):Ni_(x)Mn_(y)M_(z)(OH)_(2+α) (in Formula (1), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and x, y, z, and α satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8,x+y+z=1.0, and 0≤α≤0.4) and contains a secondary particle formed of aplurality of flocculated primary particles. The method includes acrystallization process of forming a nickel-manganese compositehydroxide by neutralizing a salt containing at least nickel and a saltcontaining at least manganese in an aqueous reaction solution. In thecrystallization process, a dissolved nickel concentration in the aqueousreaction solution is controlled in a range of at least 300 mg/L and upto 1,500 mg/L, a dissolved oxygen concentration is controlled in a rangeof at least 0.5 mg/L and up to 3.5 mg/L, and a stirring power applied tothe aqueous reaction solution is controlled in a range of at least 4kW/m³ and up to 8 kW/m³.

The crystallization process preferable includes continuously adding amixed aqueous solution including nickel and manganese into a reactionvessel and overflowing slurry including nickel-manganese compositehydroxide particles formed by neutralization to recover the particles.In addition, in the crystallization process, it is preferable that aresidence time of the mixed aqueous solution in the reaction vessel beat least 3 hours and up to 15 hours.

A third aspect of the present invention provides a method for producinga positive electrode active material for a nonaqueous electrolytesecondary battery. The method includes a process of mixing thenickel-manganese composite hydroxide and a lithium compound to obtain amixture and a process of firing in which the mixture to obtain alithium-nickel-manganese composite oxide.

It is preferable that the nickel-manganese composite hydroxide beobtained by the production method described above.

A fourth aspect of the present invention provides a positive electrodeactive material for a nonaqueous electrolyte secondary battery, in whichthe active material includes a lithium-nickel-manganese composite oxidecontaining a secondary particle formed of a plurality of flocculatedprimary particles and represented by General Formula (2):Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(2+β) (in Formula (2), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and u, x, y, z, and β satisfy −0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6,0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5). When an arbitrary radial directionfrom a center of a cross section of the secondary particle toward anoutside thereof is regarded as an x-axis direction and a directionperpendicular to the x-axis direction is regarded as a y-axis direction,an orientation rate of a crystal ab plane measured by an electronbackscatter diffraction method is at least 55% in each of the x-axisdirection and the y-axis direction.

A fifth aspect of the present invention provides a positive electrodeactive material for a nonaqueous electrolyte secondary battery, in whichthe active material is represented by General Formula (2):Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(2+β) (in Formula (2), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and u, x, y, z, and β satisfy −0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6,0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5) and contains a secondary particleformed of a plurality of flocculated primary particles; and the primaryparticles have an aspect ratio of at least 2, and at least some of theprimary particles are disposed radially in a direction from a centralpart of the particle to an outer circumference thereof, a degree ofsparsity/density obtained from an image analysis result of a SEM imageof a cross section of the secondary particle is at least 0.5% and up to25%, and a particle strength is at least 70 MPa and up to 100 MPa.

Here, it is preferable that in an area within 50% of a radius of thesecondary particle from the outer circumference of the secondaryparticle toward the central part thereof, at least 50% of the primaryparticles in number relative to a total number of the primary particlespresent within this area be disposed radially. In addition, it ispreferable that a volume-average particle diameter MV be at least 5 μmand up to 20 μm, and [(D90−D10)/average particle diameter] that is anindicator to represent spread of a particle size distribution be atleast 0.7.

A sixth aspect of the present invention provides a nonaqueouselectrolyte secondary battery having a positive electrode that includesthe positive electrode active material for a nonaqueous electrolytesecondary.

Advantageous Effects of the Invention

When the nickel-manganese composite hydroxide of the present inventionis used as the precursor, the positive electrode active material for anonaqueous electrolyte secondary battery having a high battery capacity,a high output characteristic, and an excellent cycle characteristic canbe obtained; and the nonaqueous electrolyte secondary battery having apositive electrode including the positive electrode active material canbe high in the capacity and the output, and can have a long life. Inaddition, the methods for producing the nickel-manganese compositehydroxide and the positive electrode active material can be easilycarried out even in an industrial scale; and thus, industrial values ofthem are extremely high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a schematic diagram illustrating one example of thenickel-manganese composite hydroxide of the present embodiment; and FIG.1(B) is an enlarged schematic diagram of part of the nickel-manganesecomposite hydroxide.

FIG. 2 illustrates one example of the production method of thenickel-manganese composite hydroxide of the present embodiment.

FIG. 3 is a schematic diagram illustrating one example of the nonaqueouspositive electrode active material of the present embodiment.

FIG. 4 is a drawing to explain the evaluation method of the crystalorientation of the positive electrode active material by using theelectron backscatter diffraction method (EBSD).

FIG. 5 is a drawing illustrating one example of the production method ofthe nonaqueous positive electrode active material of the presentembodiment.

FIG. 6 is a picture illustrating one example of the SEM images of thesurface and the cross section of the nickel-manganese compositehydroxide of the present embodiment (Example 1).

FIG. 7 is a picture of the SEM images of the surface and the crosssection of the nickel-manganese composite hydroxide (Comparative Example2).

FIG. 8(A) is a picture illustrating one example of the SEM image of thecross section of the nickel-manganese composite hydroxide of the presentembodiment (Example 1); and FIG. 8(B) is a picture of the SEM image ofthe cross section of the nickel-manganese composite hydroxide(Comparative Example 2).

FIG. 9 is a schematic cross-sectional view of a coin-type battery usedfor the battery evaluation.

FIG. 10 is a measurement example of the impedance evaluation and aschematic explanatory drawing of the equivalent circuit used for theanalysis.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with referring to the drawings, in-depth explanation willbe given to a nickel-manganese hydroxide of the present embodiment and amethod for producing the same, and a positive electrode active materialfor a nonaqueous electrolyte secondary battery and a method forproducing the same. It should be note that in order to promoteunderstanding of each component more easily, the drawings arerepresented while emphasizing or omitting some parts thereof; and thus,the structure, shape, drawing scale, or the like may be different fromthose of the actual ones.

1. Nickel-Manganese Composite Hydroxide

FIG. 1(A) is a schematic diagram illustrating one example of thenickel-manganese composite hydroxide 1 of the present embodiment(hereinafter, this is also referred to as “composite hydroxide 1”); andFIG. 1(B) is an enlarged drawing of part of the composite hydroxide 1 inorder to explain disposition of the primary particle 2. As illustratedin FIG. 1(A), the composite hydroxide 1 contains the secondary particle3 formed of a plurality of flocculated primary particles 2. The primaryparticle 2 in the composite hydroxide 1 has a certain average aspectratio, and at least some of the primary particles 2 are disposedradially in a direction from the central part C1 of the secondaryparticle 3 to the outer circumference thereof. Here, note that thecomposite hydroxide 1 may include a small amount of the independentprimary particles 2 such as, for example, the primary particles 2 thatare not flocculated as the secondary particle 3 and the primaryparticles 2 that are dropped off from the secondary particle 3 afterhaving been flocculated.

As will be described later, the composite hydroxide 1 can be suitablyused as a precursor of the positive electrode active material 10 for anonaqueous electrolyte secondary battery (hereinafter, this material fora nonaqueous electrolyte secondary battery is also referred to as“positive electrode active material 10”. See FIG. 3). The innerstructure of the secondary particle 3 of the composite hydroxide 1 canhave a significant influence on the inner structure of the secondaryparticle 13 of the positive electrode active material 10. Therefore,when the inner structure of the secondary particle 3 of the compositehydroxide 1 is made to the one as described above, the positiveelectrode active material 10 to be obtained therefrom can also have thestructure in which at least some of the primary particles 12 aredisposed radially in a direction from the central part C2 of thesecondary particle 13 to the outer circumference thereof; and thus, whenused in the positive electrode of the battery, high charging anddischarging capacities (hereinafter, these capacities are also referredto as “battery capacity”), an excellent output characteristic, and anexcellent cycle characteristic (hereinafter, this is also referred to as“durability”) can be obtained.

The composite hydroxide 1 is represented by General Formula (1):Ni_(x)Mn_(y)M_(z)(OH)_(2+α). In Formula (1), M is at least one elementselected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W; and x, y,and z satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8, and x+y+z=1.0. In Formula(1), a satisfies 0≤α≤0.4 and is a coefficient that varies with thevalencies of the metal elements (Ni, Mn, and M) included in thecomposite hydroxide 1.

In Formula (1), x indicates the content of Ni and satisfies 0.1≤x≤0.8,and preferably 0.15≤x≤0.6. When the value of x is within the rangedescribed above, the primary particle 2 that is disposed radially can bereadily obtained. In Formula (1), y indicates the content of Mn andsatisfies 0.1≤y≤0.6, and preferably 0.1≤y≤0.4. When the value of y iswithin the range described above, the shape and disposition of theprimary particle 2 can be controlled within the intended ranges asdescribed later. Here, as will be described later, in view ofcontrolling the crystal orientation of the positive electrode activematerial to be obtained, the characters x, y, and z in General Formula(1) may also be 0.1≤x≤0.9, 0.03≤x≤0.6, and 0≤z≤0.8, respectively.

In Formula (1), when z of M is z>0, the requirements to various batterycharacteristics can be satisfied. For example, when M includes Co, thebattery capacity and the output characteristic can be further enhanced.When M is Co, z preferably satisfies 0.1≤z≤0.35.

As will be described later, after the composite hydroxide 1 is mixedwith a lithium compound, a resulting mixture is fired to form thepositive electrode active material 10. Therefore, the composition of thecomposite hydroxide 1 is succeeded to the composition of the positiveelectrode active material 10 except for lithium. Accordingly, thecomposition of the composite hydroxide 1 may be made to the same as themetal composition, but except for lithium, of the positive electrodeactive material 10 to be obtained.

The average aspect ratio of the primary particle 2 that constitutes thecomposite hydroxide 1 is at least 3, and preferably at least 5. Theaverage aspect ratio of the primary particle 2 is the ratio of the longdiameter to the short diameter of the primary particle 2 (longdiameter/short diameter). When the aspect ratio of the primary particle2 is made within the range described above, orientation of the primaryparticle 2 in the radial direction R1 can be increased, so that thesecondary particle 3 having a radial structure in which the primaryparticles 2 are disposed radially can be obtained. With this, in thepositive electrode active material 10 obtained by using the compositehydroxide 1 as the precursor thereof, the aspect ratio of the primaryparticle 12 that constitutes the secondary particle 13 can be made to atleast 2; and thus, in the secondary particle 13 of the positiveelectrode active material 10, too, the orientation of the primaryparticle 12 in the radial direction R1 can be ensured, so that theparticle structure in which the primary articles 12 are disposedradially can be obtained. In view of the degree of sparsity/density ofthe particle, the aspect ratio is preferably up to 20.

The aspect ratio of the primary particle 2 can be measured by observingthe cross section of the secondary particle 3 with a scanning electronmicroscope (hereinafter, this is also referred to as “SEM”). Inobservation of the cross section of the secondary particle 3, first, thecomposite hydroxide 1 is buried into a resin or the like, and then, itis, for example, cut to prepare the cross section sample of thesecondary particle 3, and then, the cross sections of a plurality ofsecondary particles 3 are observed. With regard to the secondaryparticle 3 to be observed, 20 particles are arbitrarily (randomly)selected in which the maximum distance d between two points on the outercircumference of the cross section of one secondary particle 3 (seeFIG. 1) is at least 80% of the volume-average particle diameter (MV) inthe cross section of a plurality of secondary particles 3, thevolume-average particle diameter being measured using a laserdiffraction scattering particle size analyzer. Next, from each of thesecondary particles 3 thereby selected, 50 primary particles 2 arefurther selected arbitrarily (randomly). The long diameter and the shortdiameter of the primary particle 2 thereby selected are measured toobtain the aspect ratio (long diameter/short diameter). Here, forexample, the long diameter is a maximum diameter of the cross section ofthe primary particle 2 observed with SEM; and the short diameter is thelongest diameter in the direction perpendicular to the maximum diameter.The aspect ratios of 50 primary particles 2 are number-averaged tocalculate the aspect ratio (average) in each secondary particle 3. Theaspect ratios of all of 20 secondary particles 3 selected arenumber-averaged to calculate the aspect ratio (average) of the entirecomposite hydroxide 1.

The long diameter of the primary particle 2 is not particularly limitedso far as the aspect ratio described above is satisfied; it is, forexample, at least 400 nm and up to 1,500 nm, and preferably at least 500nm and up to 1,200 nm. The short diameter of the primary particle 2 is,for example, at least 30 nm and up to 200 nm, and preferably at least 50nm and up to 130 nm. The primary particle 2 has mainly a plate-likeshape; and the shape of the cross section thereof is circular,elliptical, rectangular, and the like.

As can be seen in FIG. 1(A), at least some of the primary particles 2that constitute the composite hydroxide 1 are disposed radially in adirection from the central part of the secondary particle 3 to the outercircumference thereof. Here, to be disposed radially means, for example,as can be seen in FIG. 1(B), the state in which the direction of thelong diameter L of the primary particle 2 in the cross section of thecomposite hydroxide 1 is orientated in the radial direction R1 from thecentral part C1 of the secondary particle 3 to the outer circumferencethereof. Here, to be orientated in the radial direction R1 means that inthe cross section of the composite hydroxide 1, the angle difference θbetween the direction of the long diameter L of the primary particle 2and the radial direction R1 is up to 45°, and preferably up to 30°. Ascan be seen, for example, in FIG. 1(B), the angle difference 8 betweenthe direction of the long diameter L of the primary particle 2 and theradial direction R1 may be obtained from the angle between, among theradial directions from the central part C1 of the secondary particle 3to the outer circumference thereof, the radial direction R1 that passesthrough the center of the long diameter and the direction of the longdiameter L, in which the direction of the long diameter L is thedirection from one end near the central part of the secondary particle 3to the other end in the long diameter of the primary particle 2.

In addition, it is preferable that in the region R2 that is 50% of theradius from the outer circumference of the secondary particle 3 to thecentral part C1 of the particle, at least 50% of the primary particles 2in number relative to the total number of the primary particles 2 thatare present in the 50% region be radially disposed. With this, thepositive electrode active material 10 to be obtained can have theparticle structure having a further enhanced radial orientation; andthus, when used in the positive electrode of the battery, the batterycharacteristics can be enhanced. In view of further enhancement of thebattery characteristics, it is preferable that at least 70% of theprimary particles 2 be radially orientated in the 50% region.

The ratio of the primary particles 2 that are radially disposed can bemeasured by observing the cross section of the secondary particle 3 by ascanning electron microscope (hereinafter, this is also referred to as“SEM”). Namely, in a similar manner to the measurement of the aspectratio, at least 20 of the secondary particle 3 that is at least 80% ofthe volume-average particle diameter (MV) are selected in the crosssection observation. In the secondary particles 3 thus selected, 50primary particles 2 that are present in the region R2 that is 50% of theradius from the outer circumference of the secondary particle 3 to thecentral part C of the particle (whole of the primary particle 2 isincluded in the 50% radius region) are arbitrarily (randomly) selected;and in each of the secondary particles 3, the number (N1) of the primaryparticles 2 in which the direction of the long diameter L is disposedradially are measured thereby calculating the ratio of the primaryparticles 2 that are radially disposed ([N1/50]×100)(%). Then, bycalculating the number-average ratio of the primary particles 2 that areradially disposed, the above-mentioned value can be measured. When, inat least 80% of the measured secondary particles 3 (for example, atleast 16 particles when 20 particles are measured), the ratio of theprimary particles 2 that are radially disposed is at least 50%, it canbe judged that the composite hydroxide 1 has the particle structure thatthe particles are radially orientated as a whole (radial structure).

The secondary particle 3 that constitutes the composite hydroxide 1 hasthe ratio (I(101)/I(001)) of the diffraction peak intensity I(101) ofthe 101 plane to the diffraction peak intensity I(001) of the 001 plane(hereinafter, this ratio is also referred to as “peak intensity ratio”),measured by an X-ray diffraction measurement, of up to 0.15. The peakintensity indicates the orientation of each of the crystal planes. Whenthe peak intensity ratio is up to 0.15, the aspect ratio of the primaryparticle 2 tends to become larger so that the composite hydroxide 1tends to have the radial structure. In view of radially disposing theprimary particle 2 furthermore thereby enhancing the orientation of thecrystal plane, the peak intensity ratio is preferably up to 0.135. Here,the lower limit of the peak intensity ratio is not particularly limited,and it is, for example, at least 0.03.

In the composite hydroxide 1, it is preferable that a total pore volumein a pore volume distribution be at least 0.015 cm³/g and up to 0.03cm³/g. In addition, in the composite hydroxide 1, it is preferable thatthe ratio (dV(log r)) of the pore volume having the pore size of up to40 nm to the total pore volume be at least 50%. When the pore volumedistribution is made within the range described above, sintering amongthe primary particles of the positive electrode active material can besuppressed so that the strength of the secondary particle can be madeappropriate. In addition, an increase in the resistance, a decrease inthe capacity, and cracking of particles can be suppressed, these beingcaused by a decrease in the specific surface area when this is made tothe positive electrode active material 10, so that the cyclecharacteristic can be enhanced furthermore. The pore volume distributionmay be measured by a nitrogen adsorption method.

In the composite hydroxide 1, the degree of sparsity/density ispreferably at least 0.5% and up to 25%, more preferably at least 1.0%and up to 10%, while far preferably at least 2.0% and up to 7%. Withthis, the degree of sparsity/density of the positive electrode activematerial to be obtained can also be made within the range describedabove, so that a high battery capacity can be obtained. Here, “thedegree of sparsity/density” is the value represented by [(area of thevoid 4 inside the secondary particle 3/area of the cross section of thesecondary particle 3)×100] (%), obtained, for example, from the imageanalysis result of the SEM cross section image of the compositehydroxide 1, and this can be represented by [(area of the void 4)/(sumof the area of the cross section of the primary particle 2 and the areaof void 4)×100]. Here, as the degree of sparsity/density, an averagedegree of sparsity/density can be used, in which this can be obtained insuch a way that the cross sections of 20 secondary particles 3 that areat least 80% of the volume-average particle diameter (MV) are randomlyselected, and the degree of sparsity/density of each cross section ofthe secondary particle 3 is measured followed by averaging therespective values.

In the composite hydroxide 1, the volume-average particle diameter MV ispreferably at least 5 μm and up to 20 μm, and more preferably at least 6μm and up to 15 μm. Because the volume-average particle diameter of thecomposite hydroxide is succeeded to the positive electrode activematerial, by controlling this in the range described above, thevolume-average particle diameter MV of the positive electrode activematerial to be obtained can be controlled in the range of at least 5 μmand up to 20 μm; and thus, the battery using this positive electrodeactive material can competitively have a high packing density and anexcellent output characteristic.

When the volume-average particle diameter MV is less than 5 μm, thefillability of the secondary particle 3 decreases so that when this ismade to the positive electrode active material, the battery capacity perweight may be difficult to be increased. On the other hand, when thevolume-average particle diameter MV is more than 20 μm, the specificsurface area is decreased thereby decreasing the reactivity between thecomposite hydroxide 1 (precursor) and a lithium compound in the firingprocess to be described later; and thus, the positive electrode activematerial having high battery characteristics may not be obtained.

In the nickel-manganese composite hydroxide, [(D90− D10)/averageparticle diameter] that is a fluctuation indicator of the particlediameter is preferably at least 0.65, and more preferably at least 0.70.When the fluctuation indicator of the nickel-manganese compositehydroxide is within the range described above, fine particles and coarseparticles are properly mixed so that the particle fillability can beenhanced while suppressing the decreases in the cycle characteristic andthe output characteristic of the positive electrode active material tobe obtained. Here, the upper limit of the [(D90−D10)/average particlediameter] is not particularly limited; however, in view of suppressingexcessive mixing of the fine particles or the coarse particles into thepositive electrode active material, the fluctuation indicator of thenickel-manganese composite hydroxide is preferably up to 1.2, and morepreferably up to 1.0.

In the [(D90−D10)/average particle diameter], D10 means the particlediameter at which the cumulative volume reaches 10% of the total volumeof the entire particles, the cumulative volume being obtained byaccumulating the particle number in each particle diameter from a sideof the small particle diameter; and D90 means the particle diameter atwhich the cumulative volume reaches 90% of the total volume of theentire particles, the cumulative volume being obtained by similarlyaccumulating the particle number. The average particle diameter is thevolume-average particle diameter MV, which means the volume-weightedaverage particle diameter. The volume-average particle diameter MV, D90,and D10 can be measured by using a laser diffraction scattering particlesize analyzer.

2. Production Method of the Nickel-Manganese Composite Hydroxide

FIG. 2 is a drawing illustrating one example of the production method ofthe nickel-manganese composite hydroxide of the present embodiment. Whenexplaining FIG. 2, as needed a reference is made to FIG. 1, which is aschematic drawing illustrating one example of the nickel-manganesecomposite hydroxide. As can be seen in FIG. 2, the production method ofthe composite hydroxide 1 of the present embodiment includes acrystallization process of carrying out co-precipitation by neutralizinga salt containing at least nickel and a salt containing at leastmanganese in an aqueous reaction solution in a crystallization reactionvessel. In the crystallization process of the present embodiment, it isimportant to control a dissolved nickel concentration, a dissolvedoxygen concentration in the aqueous reaction solution, and a stirringpower applied to the aqueous reaction solution within respective certainranges. By controlling these factors (parameters), the particlestructure of the composite hydroxide 1 (secondary particle 3) to beobtained can be controlled.

In the crystallization process, especially because amanganese-containing salt is used, the morphology of the compositehydroxide 1 is susceptible to the dissolved oxygen concentration in theaqueous reaction solution. For example, when the dissolved oxygenconcentration in the crystallization process is low, the primaryparticle 2 has a thick plate-like shape. The composite oxide 1 formed ofthe primary particle 2 having the thick plate-like shape is prone todecrease the degree of sparsity/density. On the other hand, when thedissolved oxygen concentration is high, the primary particle 2 has afine needle-like shape or a thin plate-like shape. The composite oxidecontaining the secondary particle formed of the flocculated primaryparticles 2, the primary particles having a fine needle-like shape or athin plate-like shape, is prone to increase the degree ofsparsity/density. Accordingly, by appropriately controlling thedissolved oxygen concentration, the morphology (shape) of the primaryparticle 2 can be controlled; and as a result of it, the degree ofsparsity/density of the secondary particle 3 can be controlled. Itshould be noted that “morphology” is the characters relating to the formand structure of the primary particle 2 and/or the secondary particle 3,in which the characters include the shape, the thickness (aspect ratio),the volume-average particle diameter, the particle size distribution,the crystal structure, the tap density, and the like of the particle.

The inventors of the present invention carried out an extensiveinvestigation about the production condition of the composite hydroxide1; and as a result of it, it was found that in addition to control ofthe dissolved oxygen concentration, by further controlling the dissolvednickel concentration in the aqueous reaction solution and the stirringpower applied to the aqueous reaction solution, the morphologies of theprimary particle 2 and the secondary particle 3 are able to becontrolled more accurately. Namely, in the production method of thepresent embodiment, by controlling the dissolved nickel concentrationand the stirring power in accordance with the dissolved oxygenconcentration, the particle structure of the composite hydroxide 1 canbe controlled thereby enabling to produce the nickel-manganese compositehydroxide that can also be suitably used as the precursor of thepositive electrode active material.

Hereinafter, specific embodiments and the like of the conditions in theproduction method of the present embodiment will be explained.

(Dissolved Oxygen Concentration)

The dissolved oxygen concentration in the aqueous reaction solution isin the range of at least 0.5 mg/L, preferably in the range of at least0.5 mg/L and up to 8.0 mg/L, preferably in the range of at least 0.5mg/L and up to 3.5 mg/L, and more preferably in the range of at least0.5 mg/L and up to 3.0 mg/L. When the dissolved oxygen concentration iscontrolled within the range described above, the primary particle 2having the plate-like shape is developed so that the nickel-manganesecomposite hydroxide 1 having the radial structure can be obtained. Inaddition, by controlling the degree of sparsity/density of the secondaryparticle 3 within the desired range, the composite hydroxide that issuitable as the precursor of the positive electrode active material canbe obtained.

When the dissolved oxygen concentration in the aqueous reaction solutionis less than 0.5 mg/L, in the crystallization reaction, the oxidation ofthe transition metals is sluggish, especially the oxidation of manganeseis suppressed; and as a result, the voids inside the secondary particle3 to be obtained is decreased thereby leading to an increase in thedensity, which may result in the particle having a low reactivity with alithium compound. Therefore, the voids inside the particle of thepositive electrode active material to be obtained also decrease, whichmay result in an increase in the reaction resistance. On the other hand,when the dissolved oxygen concentration is more than 8.0 mg/L, thesecondary particle 3 to be formed becomes extremely sparse therebyleading to significant destruction of the particle form, so that theparticle fillability is prone to be significantly deteriorated.

In view of controlling the crystal orientation of thelithium-nickel-manganese composite oxide in a further proper range, itis preferable that the dissolved oxygen concentration in the aqueousreaction solution be made in the range of at least 0.6 mg/L and up to3.0 mg/L. When the dissolved oxygen concentration is within the rangedescribed above, the positive electrode active material having a furtherenhanced battery capacity can be obtained.

In addition, in the crystallization process it is preferable that thedissolved oxygen concentration be controlled so as to be constant. Forexample, the fluctuation range of the dissolved oxygen concentration ispreferably ±0.2 mg/L, and more preferably ±0.1 mg/L.

Here, the dissolved oxygen concentration may be measured by a methodsuch as a Winkler method (chemical analysis method), a diaphragmpermeation method (electrochemical measurement method), or afluorescence measurement method. The same measurement value of thedissolved oxygen concentration can be obtained with these measurementmethods; and thus, any method mentioned above may be used.

The dissolved oxygen concentration in the aqueous reaction solution canbe adjusted by introducing into a reaction vessel a gas such as an inertgas (for example, N₂ gas and Ar gas), an air, or oxygen, withcontrolling the flow rates or the composition of these gases. Here,these gases may be flowed into the space of the reaction vessel or blowninto the aqueous reaction solution. By appropriately stirring theaqueous reaction solution by using the stirring equipment such as astirring blade with the power within the range to be described later,the dissolved oxygen concentration in the whole aqueous reactionsolution can be made further uniform.

(Dissolved Nickel Concentration)

The dissolved nickel concentration (nickel ion concentration) in theaqueous reaction solution is controlled in the range of up to 1,500mg/L, preferably in the range of at least 10 mg/L and up to 1,500 mg/L,more preferably in the range of at least 300 mg/L and up to 1,500 mg/L,while far preferably in the range of at least 400 mg/L and up to 1,200mg/L, based on the temperature of the aqueous reaction solution. Whenthe dissolved nickel concentration is controlled within the rangedescribed above and other conditions are also optimized, the degree ofsparsity/density of the secondary particle and the disposition (crystaldirection) of the primary particle 2 can be controlled so that thecomposite hydroxide 1 having the radial structure can be obtained.

When the nickel concentration in the aqueous reaction solution is lessthan 10 mg/L, the growth rate of the primary particle 2 is so slow thatthe nucleus can be readily generated, thereby tending to readily resultin the secondary particle 3 having a small particle diameter and a poorsphericity. The secondary particle 3 like this is extremely poor in theparticle fillability. When the dissolved nickel concentration is lessthan 300 mg/L, the growth rate of the primary particle 2 is so fast thatthe primary particles 2 are randomly disposed, thereby occasionallyresulting in a poor development of the radial structure and a decreasein the sphericity of the secondary particle 3 so that the particlefillability (tap density and the like) is deteriorated.

When the dissolved nickel concentration in the aqueous reaction solutionis more than 1,500 mg/L, the generation rate of the composite hydroxide1 is extremely fast so that Ni remains in the filtrate; and thus, thecrystallization amount of Ni is shifted from the intended composition sothat the mixed hydroxide having an intended ratio may not be obtained.In addition, when the dissolved nickel concentration is more than 1,500mg/L, impurities included in the composite hydroxide significantlyincrease thereby leading to deterioration of the battery characteristicswhen the positive electrode active material obtained from the compositehydroxide is used in the battery.

The dissolved nickel concentration may be controlled by adjusting pH orconcentration of a complexing agent such as, for example, concentrationof an ammonium ion in the aqueous reaction solution with controlling thetemperature of the aqueous reaction solution and the atmosphere insidethe reaction vessel within respective certain ranges. In addition, inthe crystallization process it is preferable to control the dissolvednickel concentration so as to be constant. The fluctuation range of thedissolved nickel concentration may be made, for example, within ±20mg/L. The dissolved nickel concentration may be measured by chemicallyanalyzing the Ni amount in a liquid component of the aqueous reactionsolution, for example, with an ICP emission spectrometry.

(Stirring Power)

The stirring power loaded to the aqueous reaction solution is made, forexample, in the range of at least 4 kW/m³ and up to 8 kW/m³, andpreferably in the range of at least 5 kW/m³ and up to 7.5 kW/m³. Whenthe stirring power is made within the range described above, excessiverefinement or coarsening of the secondary particle 3 can be suppressedso that the particle structure of the composite hydroxide 1 can be maderadial, and that the degree of sparsity/density and the particle sizedistribution can be made suitable. In the crystallization process, it ispreferable that the stirring power be controlled so as to be constant.The fluctuation range of the stirring power may be made, for example,within ±0.2 kW/m³. The stirring power is controlled within the rangedescribed above by adjusting the size, the rotation number, and the likeof the stirring equipment such as a stirring blade disposed in thereaction vessel.

(Reaction Temperature)

The temperature of the aqueous reaction solution inside thecrystallization reaction vessel is preferably in the range of at least35° C. and up to 60° C., and more preferably in the range of at least38° C. and up to 50° C. When the temperature of the aqueous reactionsolution is higher than 60° C., priority of the nucleus generationversus the particle growth in the aqueous reaction solution rises, sothat the shape of the primary particle 2 that constitutes the compositehydroxide 1 may be too fine. When the composite hydroxide 1 like this isused, there is a problem in that the fillability of the positiveelectrode active material 10 to be obtained is deteriorated. On theother hand, when the temperature of the aqueous reaction solution islower than 35° C., there is a tendency that the particle growth is moredominant than the nucleus generation in the aqueous reaction solution;and thus, the shapes of the primary particle 2 and the secondaryparticle 3 that constitute the composite hydroxide 1 are prone to becoarse. When the composite hydroxide 1 having the coarse secondaryparticle 3 like this is used as the precursor of the positive electrodeactive material 10, there is a problem in that the positive electrodeactive material containing particles that are so large and coarse thatirregular surface is generated when producing the electrode is formed.In addition, when the temperature of the aqueous reaction solution islower than 35° C., there is a problem of a very poor reaction efficiencybecause remaining amounts of the metal ions in the aqueous reactionsolution are so high; and moreover, the problem is prone to be causedthat the composite hydroxide including large amounts of impurityelements is formed.

(pH Value)

The pH value of the aqueous reaction solution is preferably in the rangeof at least 10.0 and up to 13.0 based on the solution temperature at 25°C. When the pH value is within the range described above, morphology ofthe secondary particle can be properly controlled with controlling thesize and shape of the primary particle 2 thereby controlling the degreeof sparsity/density in the intended range, so that the compositehydroxide that is further suitable as the precursor of the positiveelectrode active material can be obtained. When the pH value is lessthan 10.0, the generation rate of the composite hydroxide 1 becomesextremely slow so that nickel remains in the filtrate therebyoccasionally causing significant deviation of the composition of theobtained composite hydroxide from the target values thereof. On theother hand, when the pH value is more than 13.0, the particle growthrate is so fast that the nucleus can be readily generated therebyreadily tending to the particle having a small particle diameter and apoor sphericity.

(Other Conditions)

The production method of the present embodiment includes thecrystallization process of forming the nickel-manganese compositehydroxide particle by neutralizing the salts including at least nickeland manganese in the aqueous reaction solution. In the specificembodiment of the crystallization process, for example, the pH value iscontrolled by neutralization with an addition of a neutralizing agent(for example, an alkali solution or the like) to a mixed aqueoussolution including at least nickel (Ni) and manganese (Mn) in thereaction vessel with stirring the mixed solution, so that particles ofthe composite hydroxide 1 can be formed by co-precipitation.

In the production method of the present embodiment, any of acrystallization method based on a batch method and a continuouscrystallization method may be employed. Here, the continuouscrystallization method is the crystallization method in which whilecontinuously feeding the mixed aqueous solution described above, pH iscontrolled by feeding the neutralizing agent, whereby the compositehydroxide particles thus produced is recovered by overflowing. In thecontinuous crystallization method, particles having a broader particlesize distribution as compared with the batch method can be obtained, sothat the particles having a high fillability are prone to be obtained.In addition, the continuous crystallization method is suitable for massproduction, so that this is an industrially advantageous productionmethod, too. For example, when production of the composite hydroxide ofthe present embodiment is carried out by the continuous crystallizationmethod, the fillability (tap density) of the composite hydroxideparticles to be obtained can be improved furthermore, so that thecomposite hydroxide 1 having further improved fillability and degree ofsparsity/density can be produced conveniently and massively.

In the crystallization process, in the case where the continuouscrystallization method is employed, the residence time of the mixedaqueous solution in the reaction vessel is preferably in the range of 3to 15 hours, and more preferably in the range of 5 to 12 hours. Here,the residence time represents the period during which the mixed aqueoussolution stays in the reaction vessel after it is dropped into thevessel; and thus, this can be obtained by dividing the volume of thereaction vessel with the feeding rate of the mixed aqueous solution. Forexample, if the mixed aqueous solution is dropped into a 50-L reactionvessel with the feeding rate of 50 mL/min, the residence time of themixed aqueous solution in the vessel is about 16 hours. The residencetime has an influence on the particle growth and the production amount.When the residence time is shorter than 3 hours, not only the sphericitydeteriorates but also the particle diameter of the composite hydroxidemay be too small. On the other hand, when the residence time is longerthan 15 hours, growth of not only the secondary particle but also theprimary particle is prone to be significantly facilitated, so that itbecomes difficult to obtain the secondary particle having the primaryparticles orientated radially. In addition, when the residence time islonger than 15 hours, the specific surface area of the secondaryparticle 3 to be obtained is prone to be so small that the reactivitywith the Li compound may decrease and the productivity may significantlydecrease.

With regard to the mixed aqueous solution, an aqueous solution includingat least nickel and manganese, namely, an aqueous solution having atleast a nickel salt and a manganese salt dissolved therein may be used.The mixed aqueous solution may further include M; and thus, an aqueoussolution having a nickel salt, a manganese salt, and an M-including saltdissolved therein may be used. With regard to the nickel salt, themanganese salt, and the M-including salt, for example, at least one saltselected from the group consisting of sulfate, nitrate, and chloride maybe used. Among them, in view of a cost as well as a waste watertreatment, sulfate salts are preferably used.

Concentration of the mixed aqueous solution is preferably in the rangeof at least 1.0 mol/L and up to 2.4 mol/L, and more preferably in therange of at least 1.2 mol/L and up to 2.2 mol/L, as a total of the metalsalts dissolved therein. When the concentration of the mixed aqueoussolution as a total of the metal salts dissolved therein is less than1.0 mol/L, there is a risk that the primary particle that constitutesthe composite hydroxide (secondary particle) does not grow sufficientlywell because the concentration is too low. On the other hand, when theconcentration of the mixed aqueous solution is more than 2.4 mol/L,because the concentration is higher than a saturated concentration at anormal temperature, there is a risk that crystals are reprecipitatedthereby clogging a pipe and so forth. In addition, in this case, thenucleus generation of the primary particle increases so that there is arisk that the ratio of fine particles in the composite hydroxideparticles to be obtained increases. Here, the composition of the metalelements included in the mixed aqueous solution coincides with thecomposition of the metal elements included in the composite hydroxide 1to be obtained. Accordingly, the composition of the metal elements inthe mixed aqueous solution can be adjusted so as to be the same as thecomposition of the metal elements of the target composite hydroxide 1.

With regard to the neutralizing agent, an alkali solution may be used;for example, an aqueous solution of a general alkali metal hydroxidesuch as sodium hydroxide or potassium hydroxide may be used. Among them,in view of a cost and a handling easiness, a sodium hydroxide aqueoussolution is preferably used. Here, the alkali metal hydroxide may beadded directly into the aqueous reaction solution; however, in view ofeasy control of pH, it is added preferably as the aqueous solutionthereof. In this case, concentration of the alkali metal hydroxideaqueous solution is preferably in the range of at least 12% by mass andup to 30% by mass, and more preferably in the range of at least 20% bymass and up to 30% by mass. When concentration of the alkali metalhydroxide aqueous solution is less than 12% by mass, the supply amountthereof to the reaction vessel increases, so that there is a risk ofinsufficient particle growth. On the other hand, when concentration ofthe alkali metal hydroxide aqueous solution is more than 30% by mass,the pH value becomes locally high depending on the addition position ofthe alkali metal hydroxide, so that there is a risk of generation offine particles.

Together with the neutralizing agent, a complexing agent may also beadded into the mixed aqueous solution. The complexing agent is notparticularly limited so far as it can form a complex in an aqueoussolution by bonding to metal elements such as a nickel ion and amanganese ion. For example, as the complexing agent, anammonium-ion-providing body may be cited. The ammonium-ion-providingbody is not particularly limited; for example, at least one solutionselected from the group consisting of an aqueous ammonium solution, anaqueous ammonium sulfate solution, an aqueous ammonium carbonatesolution, an aqueous ammonium fluoride solution, and an aqueous ammoniumchloride solution may be used. Among these, in view of easy handling,the aqueous ammonium solution is preferably used. In the case when theammonium-ion-providing body is used, the ammonium ion concentration ismade preferably in the range of at least 5 g/L and up to 25 g/L.

In the production method of the present embodiment, it is preferable toinclude a washing process after the crystallization process. Thiswashing process is a process of washing out the impurities included inthe composite hydroxide 1 obtained in the crystallization process with awashing solution. It is preferable to use purified water as the washingsolution. The amount of the washing solution is preferably, for example,at least 1 L relative to 300 g of the composite hydroxide 1. When theamount of the washing solution relative to 300 g of the compositehydroxide 1 is less than 1 L, washing thereof is insufficient, so thatthe impurities may be left in the composite hydroxide 1. The washing maybe carried out, for example, by pouring the washing solution such aspurified water to a filtration machine such as a filter press. In thecase when SO₄ that is left in the composite oxide 1 is wanted to bewashed out furthermore, it is preferable to use sodium hydroxide, sodiumcarbonate, or the like as the washing solution.

3. Positive Electrode Active Material for a Nonaqueous ElectrolyteSecondary Battery

FIG. 3 is a drawing illustrating one example of the positive electrodeactive material 10 for a nonaqueous electrolyte secondary battery of thepresent embodiment (hereinafter, this material for a nonaqueouselectrolyte secondary battery is also referred to as “positive electrodeactive material 10”). The positive electrode active material 10 can berepresented by General Formula (2): Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(2+β) (inFormula (2), M is at least one additional element selected from Co, Ti,V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W; and u, x, y, z, and β satisfy−0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5). InFormula (2), β is a coefficient that varies in accordance with the ratioof the lithium atom to the metal elements other than lithium included inthe positive electrode active material 10 and with the valencies of themetal elements other than lithium.

As can be seen in FIG. 3, the positive electrode active material 10contains the secondary particle 13 formed of a plurality of flocculatedprimary particles 12. Although the positive electrode active material 10mainly contains the secondary particle 13 formed of a plurality offlocculated primary particles 12, this may also include small amount ofthe primary particle 2 that is present independently, as in the case ofthe composite hydroxide 1.

As in the case of the composite hydroxide 1, the positive electrodeactive material 10 has the particle structure in which at least some ofthe primary particles 12 are disposed radially in a direction from thecentral part of the secondary particle 13 to the outer circumferencethereof (radial structure). The aspect ratio of a plurality of primaryparticles 12 is preferably at least 2. It is preferable that at leastsome of the primary particles 12 be disposed radially from the centralpart of the secondary particle 13 to the outer circumference thereof.

Because the positive electrode active material 10 has the radialstructure, the electrolyte solution can readily penetrate into insidethe positive electrode active material 10; and in addition, the stressload caused by expansion and shrinkage of the positive electrode activematerial upon charging and discharging can be relaxed in the particleboundary of the primary particles 12; and thus, the cycle characteristiccan be enhanced. Namely, in the primary particle 12, the expansion andshrinkage increases from the central part C2 toward the outercircumference thereby decreasing the stress that is accumulated in thesecondary particle 13; and thus, destruction of the secondary particle13 is reduced so that the cycle characteristic is enhanced. Because ofthis, when the positive electrode active material 10 is used in thepositive electrode of the secondary battery, high charging anddischarging capacities (hereinafter, these capacities are also referredto as “battery capacity”) as well as an excellent cycle characteristic(hereinafter, this is also referred to as “durability”) can beexhibited.

FIG. 4(A) and FIG. 4(B) are the drawings to explain the evaluationmethod of the crystal orientation of the positive electrode activematerial 10 by using the electron backscatter diffraction method (EBSD).In EBSD, by using a scanning electron microscope (SEM), an electron beamis irradiated to a sample, and the Kikuchi pattern thereby formed in thesample's plane to be measured due to a diffraction phenomenon of theelectron beam is analyzed so that the crystal direction and the like ofa minute portion thereof can be measured. By analyzing the crystaldirection measured by EBSD, the crystal orientation in a specificdirection can be evaluated.

In this specification, an arbitrary radial direction from a center C2 ofa cross section of the secondary particle 13, which constitutes thepositive electrode active material 10, toward an outer circumferencethereof is regarded as an x-axis direction and a direction perpendicularto the x-axis direction is regarded as a y-axis direction; and wherebyan evaluation of the crystal orientation using EBSD is carried out.Hereinafter, each direction will be explained by referring to FIG. 4(A).

For example, as illustrated in FIG. 4(A), when the observation crosssection is regarded as the paper surface, the x-axis direction in thecross section of the secondary particle 13 is the direction toward ahorizontal direction from the center C2 in the observation crosssection. Also, when the observation cross section is regarded as thepaper surface, the y-axis direction in the cross section of thesecondary particle 13 is the direction toward a perpendicular directionfrom the center C2 in the observation cross section. The z-axisdirection is the vertical direction from the center C2 in theobservation cross section.

In the positive electrode active material 10 according to the presentembodiment, the orientation rate of the crystal ab plane measured byEBSD is preferably at least 55% in each of the x-axis direction and they-axis direction. In addition, it is more preferable that theorientation rate of the crystal ab plane be at least 80% in at least oneof the x-axis direction and the y-axis direction. When the orientationrate of the crystal ab plane is within the range described above, thebattery capacity can be enhanced furthermore. Here, the upper limit ofthe orientation rate of the crystal ab plane is not particularlylimited, and it is up to 95%.

The lithium-nickel-manganese composite oxide (positive electrode activematerial 10) has a hexagonal crystal structure, and it also has alayered structure in which a transition metal ion layer formed ofnickel, manganese, and the like and a lithium ion layer are alternatelystacked in a c-axis direction. Here, when the secondary battery ischarged and discharged, the lithium ion in the crystal that constitutesthe positive electrode active material 10 migrates to a [100]-axisdirection or a [110]-axis direction (ab plane), and thereby the lithiumion is inserted and de-inserted. Accordingly, although the detail is notyet clear, it is presumed that when the orientation rates of the crystalab plane in the x-axis direction and the y-axis direction each arewithin the range described above, the lithium ion can be inserted andde-inserted further readily in the positive electrode active material 10thereby leading to further enhancement of the battery capacity.

On the other hand, in the positive electrode active material having thestructure in which the primary particles are randomly flocculated, forexample, as described in Comparative Examples to be described later (seeFIG. 7(B)), the orientation rate of the crystal ab plane in at least oneof the x-axis direction and the y-axis direction is less than 55%, whilethe orientation rate in the c-axis direction increases. In this case,the battery capacity may be insufficient in the positive electrodeactive material 10 in the secondary battery (positive electrode).

Here, EBSD-based evaluation is carried out as follows. Namely, in thecross section observation of the secondary particle 13, at least 3 ofthe secondary particle 13 that is at least 80% of the volume-averageparticle diameter (MV) are selected; and the orientation rates of the abplane in the x-axis direction and the y-axis direction of each particleare measured followed by averaging these measured values. With regard toa specific EBSD-based evaluation method, the method described in Exampleto be described later may be used.

In the primary particle 12, it is preferable that in the area within 50%of the radius from the outer circumference of the secondary particletoward the central part C2 of the particle, at least 50% of the primaryparticles 12 in number be disposed radially in the direction from thecenter side of the particle toward the outer circumference thereof. Withthis, the positive electrode active material 10 can have the particlestructure having a further enhanced radial orientation (radialstructure) so that the battery characteristics can be further enhancedwhen used in the positive electrode of the battery. In order to enhancethe battery characteristics furthermore, it is more preferable that atleast 70% of the primary particles in number in the 50% region bedisposed radially.

The aspect ratio of the primary particle 12, namely the ratio of thelong diameter to the short diameter of the primary particle 12 (longdiameter/short diameter) is more preferably at least 2. When the aspectratio is made to at least 2, orientation of the primary particle 12 ofthe positive electrode active material 10 can be enhanced, so that thesecondary particle 13 can have the radial structure. In view of thedegree of sparsity/density of the secondary particle 13, the aspectratio is preferably up to 20, and more preferably up to 10. The particlestructure of the primary particle 12, namely, the disposition and theaspect ratio of the primary particle 12 can be measured by observationof the cross section of the secondary particle 13 with a scanningelectron microscope, as in the case of the composite hydroxide 1.

The long diameter of the primary particle 12 is not particularly limitedso far as the aspect ratio described above is satisfied. The longdiameter is, for example, at least 500 nm and up to 1,500 nm, andpreferably at least 600 nm and up to 1,400 nm. The short diameter of theprimary particle 12 is, for example, at least 200 nm and up to 500 nm,and preferably at least 250 nm and up to 400 nm. The primary particle 12has mainly a plate-like shape; and the shape of the cross sectionthereof is circular, elliptical, rectangular, and so forth.

In the positive electrode active material 10, the particle strength isat least 70 MPa and up to 100 MPa, and preferably at least 75 MPa and upto 95 MPa. With this, while having an enough strength to resist thestress that is generated by the expansion and shrinkage caused bycharging and discharging, the stress can be relaxed by releasing thegenerated stress, so that the cycle characteristic can be enhanced. Theparticle strength can be measured by applying a load to the particlewith an indenter using a micro-strength assessment apparatus followed bycalculation of the particle strength at the time when the particle isbroken.

In the positive electrode active material 10, the degree ofsparsity/density is preferably at least 0.5% and up to 25%, and morepreferably at least 1.0% and up to 10. With this, the penetration of theelectrolyte solution into inside the secondary particle as well as therelaxation of the stress generated by the expansion and shrinkage causedby charging and discharging can be improved. Here, “the degree ofsparsity/density” is, for example, the value represented by [(area ofthe void 4 inside the secondary particle 3/area of the cross section ofthe secondary particle 3)×100] (%), obtained from the image analysisresult of the cross section SEM image of the positive electrode activematerial 10. The degree of sparsity/density may be obtained in the sameway as the method for measurement of the degree of sparsity/density ofthe composite hydroxide 1.

In the positive electrode active material 10, the volume-averageparticle diameter MV is preferably at least 5 μm and up to 20 μm, andmore preferably at least 6 μm and up to 15 μm. With this, the decreasein the specific surface area can be suppressed while retaining thefillability high; and thus, the battery using this positive electrodeactive material can be competitive in the high packing density and theexcellent output characteristic.

In the positive electrode active material 10, [(D90− D10)/averageparticle diameter] that is an indicator to represent fluctuation of theparticle diameter is preferably at least 0.70. When the fluctuationindicator of the nickel-manganese composite hydroxide is within therange described above, fine particles and coarse particles are mixed toa suitable degree; and thus, the particle fillability can be enhancedwith suppressing deterioration of the cycle characteristic and theoutput characteristic of the positive electrode active material to beobtained. In view of suppressing excessive mixing of the fine particlesor the coarse particles into the positive electrode active material, thefluctuation indicator of the nickel-manganese composite hydroxide ispreferably up to 1.2, and more preferably up to 1.0.

In the positive electrode active material 10, the tap density ispreferably at least 2.3 g/cm³ and up to 2.8 g/cm³, and more preferablyat least 2.4 g/cm³ and up to 2.7 g/cm³. When the tap density is withinthe range described above, the fillability becomes excellent, and thus,the battery capacity can be enhanced.

4. Method for Producing the Positive Electrode Active Material for aNonaqueous Electrolyte Secondary Battery

The production method of the present embodiment is the method forproducing the positive electrode active material including thelithium-nickel-manganese composite oxide represented by General Formula(2): Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(2+β) (in Formula (2), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and u, x, y, z, and β satisfy −0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6,0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5) and containing the secondary particleformed of a plurality of flocculated primary particles.

FIG. 5 is a drawing illustrating one example of the production method ofthe positive electrode active material for a nonaqueous electrolytesecondary battery of the present embodiment (hereinafter, this materialfor a nonaqueous electrolyte secondary battery is also referred to as“positive electrode active material”). As illustrated in FIG. 5, theproduction method includes a process of mixing the composite hydroxide 1produced by the production method described above with a lithiumcompound to obtain a mixture of these and a firing process of firing themixture to obtain a lithium-nickel-manganese composite oxide. When thepositive electrode active material 10 that is obtained using thecomposite hydroxide 1 as the precursor thereof is used in the secondarybattery, the battery capacity, the output characteristic, and the cyclecharacteristic are so good that the industrial value thereof is veryhigh. Hereinafter, the production method of the positive electrodeactive material 10 will be explained.

Here, the precursor of the positive electrode active material 10 mayinclude, besides the composite hydroxide 1, a small amount of theindependent primary particle 2 such as, for example, the primaryparticle 2 that is not flocculated as the secondary particle 3 and theprimary particle 2 that is dropped off from the secondary particle 3after having been flocculated; and in addition, the precursor mayinclude compounds other than the composite hydroxide 1 of the presentembodiment, such as, for example, a nickel composite hydroxide, so faras the effects of the present invention are not impaired by the additionthereof.

(Mixing Process)

First, the composite hydroxide 1 is mixed with a lithium compound toform a mixture of these. The lithium compound is not particularlylimited, and heretofore known lithium compounds may be used. Forexample, in view of easy availability, lithium hydroxide, lithiumnitrate, lithium carbonate, lithium chloride, or a mixture of these maybe preferably used. Among them, in view of easy handling, stablequality, and low contamination of impurities, lithium hydroxide andlithium carbonate are more preferable as the lithium compound. Prior tothe mixing process, the composite hydroxide 1 may be oxidized therebyconverting at least part thereof to a nickel-manganese composite oxide,and then, this may be mixed.

The composite hydroxide 1 and the lithium compound are mixed such thatthe ratio (Li/Me) of the number of the lithium atom (Li) to the numberof metal atoms other than lithium in the lithium mixture, namely, thetotal atom number of nickel, cobalt, and additional elements other thanlithium (Me), may be at least 0.95 and up to 1.50, and preferably atleast 0.95 and up to 1.20. Namely, because the Li/Me ratio does notchange before and after firing, the mixing ratio of Li/Me in the mixingprocess becomes the Li/Me ratio in the positive electrode activematerial; and thus, the mixing is carried out such that the Li/Me ratioin the mixture may be the same as the Li/Me ratio in the positiveelectrode active material to be obtained.

For mixing, a general mixing machine such as, for example, a shakermixer, a Lodige mixer, a Julia mixer, a V blender, or the like may beused, so far as the mixing can be sufficiently made such that the shapeand structure of the composite oxide 1 is not destroyed.

(Firing Process)

Next, the lithium mixture is fired to obtain thelithium-nickel-manganese composite oxide. Firing is carried out, forexample, in an oxidative atmosphere at the temperature of at least 700°C. and up to 1100° C., and preferably at least 800° C. and up to 1000°C. When the firing temperature is lower than 700° C., the firing isinsufficient so that the tap density may deteriorate. In addition, whenthe firing temperature is lower than 700° C., diffusion of lithium isinsufficient so that excess lithium remains; as a result, the crystalstructure may not be well formed, and uniformity of the composition ofnickel, manganese, and so forth in the particle is not sufficient, sothat satisfactory characteristics may not be obtained when used in thebattery. On the other hand, when the firing temperature is higher than1100° C., a sparse portion in the particle surface may be densified. Inaddition, when the firing temperature is higher than 1100° C., thelithium-nickel-manganese composite oxide may be severely sintered amongthe particles thereof, and an abnormal grain growth may take place; andthus, the nearly spherical particle morphology may not be retainedbecause the particles are coarsened after having been fired. In thepositive electrode active material like this, the specific surface areathereof is decreased. Therefore, when this is used in the battery, thereappears a problem of decrease in the battery capacity due to increase inthe positive electrode resistance. In addition, when the firingtemperature is higher than 1100° C., the Li site and the transitionmetal site are mixed so that the battery characteristics may bedeteriorated.

The firing time is not particularly limited, and it is at least about 1hour and up to about 24 hours. It is preferable that the mixture beretained, for example, at the maximum attained temperature of at least800° C. and up to 1000° C. for a period of at least 2 hours.

In view of uniformly carrying out the reaction between the lithiumcompound and the composite hydroxide 1 or the nickel-manganese compositeoxide obtained by oxidizing the composite hydroxide, the temperatureraising rate is preferably, for example, in the range of at least 1°C./minute and up to 10° C./minute until the firing temperature.

In addition, before firing, when the mixture is kept at the temperaturearound the melting point of the lithium compound for a period of about 1hour to about 10 hours, the reaction can be carried out furtheruniformly. For example, before firing, it is preferable that thetemperature be raised to at least 650° C. and up to 750° C., thetemperature below the firing temperature, and then kept in thistemperature range for the period not longer than 6 hours to carry outcalcination. When the holding time in calcination is longer than 6hours, the crystallinity of the lithium-transition metal oxide afterhaving been fired may decrease.

The furnace to be used in firing is not particularly limited, so thatany furnace may be used so far as the lithium mixture can be fired in astream of an air or of oxygen; however, an electric furnace notgenerating a gas is preferable. Here, any of a batch method and acontinuous method may be used.

In the lithium-transition metal composite oxide obtained by firing,sintering among the particles is suppressed; however, occasionally,coarse particles are formed due to light sintering or flocculation. Inthis case, additionally the lithium-nickel-manganese composite oxidethereby obtained may be crushed. By crushing, the sintering andflocculation may be dissolved, so that the particle size distributionmay be adjusted.

In the production method of the positive electrode active material ofthe present embodiment, the composite oxide to be used may include,besides the composite hydroxide 1 containing the secondary particle 3formed of the flocculated primary particles 2, the independent primaryparticle 2 such as, for example, the primary particle 2 that is notflocculated as the secondary particle 3 and the primary particle 2 thatis dropped off from the secondary particle 3 after having beenflocculated. In addition, the composite oxide to be used may include acomposite hydroxide or a composite oxide that is obtained by oxidizingthe composite hydroxide that is produced with a method other than theabove-described method, so far as the effects of the present inventionare not impaired by the addition thereof. The positive electrode activematerial to be obtained mainly includes the lithium-nickel-manganesecomposite oxide containing the secondary particle formed of theflocculated primary particles, in which the material may includeindependent primary particles such as, for example, the primary particlethat is not flocculated as the secondary particle and the primaryparticle that is dropped off from the secondary particle after havingbeen flocculated.

5. Nonaqueous Electrolyte Secondary Battery

One example of the nonaqueous electrolyte secondary battery of thepresent embodiment will be explained with respect to each compositionelement separately. The nonaqueous electrolyte secondary battery of thepresent embodiment includes a positive electrode, a negative electrode,and a nonaqueous electrolyte solution, in which this may be composed ofthe same composition elements as those of a general lithium ionsecondary battery. It should be noted that the embodiments explainedhereinafter are mere examples, so that the nonaqueous electrolytesecondary battery may be carried out not only with the embodimentsdescribed below but with the embodiments changed or modified variouslybased on a knowledge of a person ordinarily skilled in the art. Inaddition, the nonaqueous electrolyte secondary battery is notparticularly limited in the use thereof.

(1) Positive Electrode

The positive electrode is formed of a positive electrode mixed material.Hereinafter, the positive electrode mixed material as well as eachmaterial that constitutes the mixed material will be explained. Apositive electrode mixed material paste is prepared by mixing thepositive electrode active material of the present embodiment asdescribed above with a conductive agent and a binder, and as needed, anactivated carbon, a solvent, and the like for the purpose of viscosityadjustment, followed by kneading this resulting mixture.

The mixing ratios of each material in the positive electrode mixedmaterial serve as an element to determine the performance of the lithiumsecondary battery; and thus, the ratios can be adjusted in accordancewith the use thereof. The mixing ratios of the materials may be made assame as those of publicly known positive electrodes of the lithiumsecondary battery; therefore, for example, when total mass of the solidportions in the positive electrode mixed material excluding the solventis regarded as 100% by mass, the positive electrode active material maybe included therein in the range of 60% by mass to 95% by mass, theconductive agent in the range of 1% by mass to 20% by mass, and thebinder in the range of 1% by mass to 20% by mass.

The positive electrode mixed material paste thus obtained is applied tothe surface of an electric collector made of, for example, aluminumfoil, and then it is dried to scatter the solvent off to prepare thesheet-like positive electrode. As needed, in order to increase theelectrode density, it can also be pressed with a roll-press or the like.The sheet-like positive electrode obtained in the way as described aboveis, for example, cut to a proper size in accordance with the targetbattery; and then, this can be used for fabrication of the battery.However, the preparation method of the positive electrode is not limitedto the above-mentioned example, so that it may also be prepared by othermethods.

With regard to the conductive agent to be used, for example, graphite(such as natural graphite, artificial graphite, and expandable graphite)as well as a carbon black material such as acetylene black and Ketchenblack may be used. With regard to the binder, such as, for example,polyvinylidene fluoride, polytetrafluoroethylene, an ethylene propylenediene rubber, a fluorine rubber, a styrene-butadiene, a cellulose-basedresin, and polyacrylic acid may be used.

The binder plays a role to bind the active material particles; forexample, fluorine-containing resins such as polytetrafluoroethylene,polyvinylidene fluoride, and a fluorine rubber as well as thermoplasticresins such as polypropylene and polyethylene may be used. As needed, asolvent, which can disperse the positive electrode active material, aconductive agent, and an activated carbon, and also can dissolve thebinder, is added to the positive electrode mixed material. With regardto the solvent, an organic solvent specifically such asN-methyl-2-pyrrolidone may be used. In addition, in order to increase anelectric double layer capacity, an activated carbon may be added to thepositive electrode mixed material.

(2) Negative Electrode

As the negative electrode, a metal lithium, a lithium alloy, or the likemay be used. Alternatively, a shaped article may be used as the negativeelectrode, the article being prepared in such a way that a negativeelectrode mixed material that is prepared by mixing a binder with anegative electrode active material capable of inserting and de-insertinga lithium ion followed by addition of a suitable solvent so as to makeit a paste-like form, is applied to the surface of an electric collectormade of metal foil such as copper foil, and then, it is dried and, asneeded, compressed in order to increase the electrode density.

With regard to the negative electrode active material, for example,natural graphite, artificial graphite, a fired body of an organiccompound such as a phenol resin, or a powdery body of a carbon substancesuch as cokes may be used. In this case, similarly to the positiveelectrode, among others a fluorine-containing resin such aspolyvinylidene fluoride may be used as the negative electrode binder;and as the solvent to disperse the active material and the binder, anorganic solvent such as N-methyl-2-pyrrolidone may be used.

(3) Separator

Between the positive electrode and the negative electrode, a separatoris interposed, and then it is disposed. The separator separates betweenthe positive electrode and the negative electrode, and it also storesthe electrolyte, in which publicly known materials may be used; forexample, a thin film that is made of polyethylene, polypropylene, or thelike and has many fine pores may be used.

(4) Nonaqueous Electrolyte Solution

The nonaqueous electrolyte solution is obtained by dissolving a lithiumsalt as a supporting salt in an organic solvent. Illustrative example ofthe organic solvent includes cyclic carbonates such as ethylenecarbonate, propylene carbonate, butylene carbonate, andtrifluoropropylene carbonate; linear carbonates such as diethylcarbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropylcarbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxy ethane; sulfur compounds such as ethylmethyl sulfone and butane sultone; and phosphorous compounds such astriethyl phosphate and trioctyl phosphate, in which a single solventselected from these solvents or a mixture of two or more of them may beused.

With regard to the supporting salt, LiPF₆, LiBF₄, LiClO₄, LiAsF₆,LiN(CF₃SO₂)₂, composite salts of them, or the like may be used.Furthermore, the nonaqueous electrolyte solution may include a radicalscavenger, a surfactant, a flame retardant, and so forth.

(5) Form and Composition of the Battery

The form of the lithium secondary battery of the present invention thatincludes the positive electrode, the negative electrode, the separator,and the nonaqueous electrolyte solution as explained above is notparticularly limited; and thus it can have various forms such as acylindrical form and a laminate form. In any form used, the positiveelectrode and the negative electrode are laminated via the separator toform an electrode body; then, the electrode body thus obtained isimpregnated with the nonaqueous electrolyte solution. Then, between apositive electrode collector and a positive electrode terminal leadingto outside, and between a negative electrode collector and a negativeelectrode terminal leading to outside are connected by a collector leador the like. Then, the composition thus formed is sealed in a batterycase thereby completing the battery.

EXAMPLES Example 1 [Preparation of Composite Hydroxide]

Prescribed amount of purified water was taken into a reaction vessel(50L); the stirring power was set at 6.0 kW/m²; and with stirring, thetemperature inside the vessel was set at 42° C. At this time, inside thereaction vessel was made to a non-oxidative atmosphere (oxygenconcentration: 1% by volume) thereby adjusting the dissolved oxygenconcentration in the solution in the reaction vessel at 1.0 mg/L. Intothis reaction vessel were continuously and simultaneously added a 2.0 Mmixed aqueous solution including nickel sulfate, cobalt sulfate, andmanganese sulfate with the molar ratio ofnickel:cobalt:manganese=46:30:24, an alkali solution of a 25% by massaqueous sodium hydroxide solution, and a complexing agent of a 25% bymass aqueous ammonia solution so as to make the aqueous reactionsolution. The pH value and the ammonium ion concentration werecontrolled such that the dissolved nickel concentration might becomeconstant at 400 mg/L. At this time, in the reaction vessel, the pH valuewas 11.8 and the ammonium ion concentration was in the range of 12 to 15g/L. The flow rate of the mixed aqueous solution was controlled so thatthe residence time thereof in the reaction vessel might become 8 hours.After the neutralization crystallization reaction was stabilized, theslurry including the nickel-cobalt-manganese composite hydroxide wasrecovered from the overflow port; and then, a cake of thenickel-cobalt-manganese composite hydroxide was obtained by suctionfiltration (crystallization process). Impurities included therein werewashed out by pouring 1 L of purified water to 140 g of thenickel-cobalt-manganese composite hydroxide present in the filtrationequipment that was used for filtration to obtain thenickel-cobalt-manganese composite hydroxide (washing process).

The structures of the surface and of the cross section of thenickel-cobalt-manganese composite hydroxide thereby obtained wereobserved with a scanning electron microscope. As a result, it wasconfirmed that the aspect ratio was at least 3 and that the primaryparticles were disposed radially from inside of the particles to outsidethereof (FIG. 6A: surface, FIG. 6B: cross section). In addition, in the50% region of the radius from the outer circumference of the secondaryparticle to the central part of the secondary particle, at least 50% ofthe primary particles were disposed radially.

As a measurement result of the nickel-cobalt-manganese compositehydroxide with an X-ray diffraction method, it was confirmed that theratio (I(101)/I(001)) was 0.094, I(101) being the diffraction peakintensity of the 101 plane, and I(001) being the diffraction peakintensity of the 001 plane. In addition, it was confirmed that thevolume-average particle diameter MV of the nickel-cobalt-manganesecomposite hydroxide was 8.2 μm, and that [(D90−D10)/average particlediameter] was 0.8. In addition, as a result of the pore volumedistribution measurement, it was confirmed that the total pore volume ofthe nickel-cobalt-manganese composite hydroxide was 0.021 cm³/g, and theratio (dV(log r)) of the pore volume having the pore size of up to 40 nmwas 65%. In order to assess the degree of sparsity/density, the particlecross section and the void area within the particle were obtained byusing an image analysis software (WinRoof 6.1.1); and then, the degreeof sparsity/density was calculated from the equation [(void area withinthe particle)/(particle cross section)×100] (%). Twenty cross sectionsof the secondary particles that were at least 80% of the volume-averageparticle diameter (MV) were arbitrarily selected, and the degree ofsparsity/density of each of the cross sections of the secondaryparticles was measured; and the average value thereof (average degree ofsparsity/density) was calculated to be 3.8%. After the obtainednickel-cobalt-manganese composite hydroxide was dissolved into aninorganic acid, the chemical analysis thereof was carried out with anICP emission spectrometry; and as a result, the composition thereof wasNi_(0.46)Co_(0.30)Mn_(0.24)(OH)₂. The characteristics of the obtainedcomposite hydroxide are listed in Table 1.

[Preparation of the Positive Electrode Active Material]

After the nickel-cobalt-manganese composite hydroxide and lithiumcarbonate were weighed so as to give the Li/Me ratio of 1.02, they werefully mixed to obtain a lithium mixture by using a shaker mixer (TURBULAType T2C; manufactured by Willy A. Bachofen AG (WAB)) with applying astrength that the shape and structure of the precursor were able to bestill retained (mixing process).

The lithium mixture thus obtained was inserted into a magnesia-madefiring vessel, and by using a sealed-type electric furnace, thetemperature thereof was raised in an air atmosphere with the flow ratethereof being 10 L/minute and with the temperature raising rate of 2.77°C./minute until 900° C., at which temperature the mixture was kept for10 hours; and then, it was cooled in the furnace to room temperature toobtain the lithium-transition metal composite oxide (firing process).

By observation of the cross section of the obtained positive electrodeactive material with a scanning electron microscope, it was confirmedthat the primary particles having the aspect ratio of at least 2 wereorientated from the inside of the particle to the outside thereof (FIG.8(A)). It was confirmed that the volume-average particle diameter MV ofthe positive electrode active material was 7.9 μm, and[(D90-D10)/average particle diameter] thereof was 0.8. Evaluationresults of other powder characteristics are listed in Table 2.

[Fabrication and Evaluation of the Battery]

After 52.5 mg of the obtained positive electrode active material, 15 mgof acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE)were mixed, the resulting mixture was press molded with the appliedpressure of 100 MPa to prepare the positive electrode (electrode forevaluation) PE having the diameter of 11 mm and the thickness of 100 μm,as depicted in FIG. 9. The positive electrode PE thus prepared was driedat 120° C. in a vacuum dryer for 12 hours. Then, the 2032 coin-typebattery CBA was prepared by using this positive electrode PE under an Aratmosphere in a globe box in which the dew point was controlled at −80°C. For the negative electrode NE, a lithium (Li) metal having thediameter of 17 mm and the thickness of 1 mm was used. For theelectrolyte solution, an equal amount mixture of ethylene carbonate (EC)and diethyl carbonate (DEC) (manufactured by Tomiyama Pure ChemicalIndustries, Ltd.) including 1-M LiClO₄ as the supporting electrolyte wasused. For the separator SE, a polyethylene porous film having the filmthickness of 25 μm was used. The coin-type battery having the gasket GAand the wave washer WW was fabricated to the battery having a coin-likeshape by using the positive electrode can PC and the negative electrodecan NC.

[Battery Evaluation]

The initial discharging capacity, the cycle capacity retention rate, andthe positive electrode resistance, used to evaluate the performance ofthe obtained coin-type battery, are defined as follows.

The initial discharging capacity was measured as follows. Namely, afterthe open circuit voltage (OCV) was stabilized by allowing to leave thecoin-type battery CBA1 for about 24 hours after it was prepared, it wascharged to the cut-off voltage of 4.3 V with the current density to thepositive electrode being 0.1 mA/cm², and after 1 hour of pause, it wasdischarged to the cut-off voltage of 3.0 V, and thereby the capacity atthis time was regarded as the initial discharging capacity.

The cycle capacity retention rate was evaluated as follows. Namely, thecycle to charge until 4.1 V and discharge until 3.0 V with the currentdensity to the positive electrode being 2 mA/cm² was repeated at 60° C.for 500 times with the 2C rate; and the capacity retention rate wasobtained by calculating the ratio of the discharging capacity after therepeat of the charging and discharging operations to the initialdischarging capacity. Measurements of the charging and dischargingcapacities were carried out by using a multi-channel voltage/electricitygenerator (R6741A; manufactured by Advantest Corp.).

The positive electrode resistance was evaluated as follows. Namely, whenthe coin-type battery CBA1 is charged with the charge voltage of 4.1 V,and the measurement is made by the alternate current impedance methodusing a frequency response analyzer and a potentiogalvanostat (1255B,manufactured by Solartron Analytical Inc.), the Nyquist plot depicted inFIG. 10 can be obtained. The Nyquist plot is represented as the sum ofthe characteristic curves showing the solution resistance, the negativeelectrode resistance and the capacity thereof, and the positiveelectrode resistance and the capacity thereof. Accordingly, based on theNyquist plot, the fitting calculation was carried out to obtain thepositive electrode resistance value by using the equivalent circuit.

When the battery evaluation was carried out with regard to the coin-typebattery having the positive electrode that was formed by using thepositive electrode active material, the initial discharging capacity of169.1 mAh/g, the positive electrode resistance of 1.84Ω, and thecapacity retention rate after 500 cycles of 78.9% were obtained.

The characteristics of the nickel-cobalt-manganese composite hydroxideobtained by this Example are listed in Table 1; and the characteristicsof the positive electrode active material and evaluation results of thecoin-type battery that is produced by using this positive electrodeactive material are listed in Table 2. The same items of Examples 1 to 4and of Comparative Examples 1 to 6, which were carried out below, arealso included in Table 1 and Table 2.

Example 2

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the nickel concentration in theaqueous reaction solution in the crystallization process was changed to600 mg/L. The evaluation results of the positive electrode activematerial thereby obtained are listed in Table 2.

Example 3

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the residence time of the mixedaqueous solution in the crystallization process was changed to 10 hours.

Example 4

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the residence time of the mixedaqueous solution in the crystallization process was changed to 6 hours.

Comparative Example 1

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the stirring power in thecrystallization process was changed to 5.0 kW/m², and the dissolvedoxygen concentration of the aqueous reaction solution was changed to 8.0mg/L.

Comparative Example 2

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the nickel concentration of theaqueous reaction solution in the crystallization process was changed to80 mg/L, and the residence time of the mixed aqueous solution waschanged to 16 hours.

Comparative Example 3

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the nickel concentration of theaqueous reaction solution in the crystallization process was changed to80 mg/L.

Comparative Example 4

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the nickel concentration of theaqueous reaction solution in the crystallization process was changed to1,500 mg/L.

Comparative Example 5

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the temperature of the aqueousreaction solution in the crystallization process was changed to 65° C.

TABLE 1 Compara. Compara. Compara. Compara. Compara. Example 1 Example 2Example 3 Example 4 Example 1 Example 2 Example 3 Example 4 Example 5Precipitation Dissolved oxygen mg/L 1.0 1.0 1.0 1.0 8.0 1.0 1.0 1.0 1.0condition concentration Dissolved Ni mg/L 400 600 400 400 400 80 80 1500400 concentration Stirring power Kw/m³ 6.0 6.0 6.0 6.0 5.0 6.0 6.0 6.06.0 Precipitation ° C. 42 42 42 42 42 42 42 42 65 temperature pH — 11.811.6 11.8 11.8 11.8 12.3 12.3 11.4 11.8 Primary Residence time hr 8 8 106 8 16 8 8 8 particle Long diameter nm 857 631 922 536 1439 437 394 798367 Short diameter nm 116 96 132 79 136 231 206 355 201 Secondary Aspectratio (long — 7.4 6.6 7.0 6.8 10.6 1.9 1.9 2.2 1.8 particlediameter/short (composite diameter) Cross section — Radial structurePorous Random flocculation structure structure structure I(101)/I(001) —0.094 0.082 0.121 0.116 0.183 0.155 0.164 0.210 0.175 Volume-average μm8.2 9.1 10.0 6.8 4.8 8.1 4.5 12.3 6.5 particle diameter MV (D90-D10)/ —0.80 0.87 0.90 0.65 0.48 0.65 0.56 0.96 0.62 average particle diameterMV Sparse density % 3.8 4.0 4.1 4.7 42.6 0.8 0.7 0.4 0.4 Total porecm³/g 0.021 0.023 0.019 0.020 0.032 0.016 0.022 0.012 0.017 volumeComposition — Ni:Co:Mn = 0.46:0.30:0.24 Ni:Co:Mn = 0.46:0.30:0.24 *1)*2) *1) Ni:Co:Mn = 0.44:0.31:0.25 *2) Ni:Co:Mn = 0.46:0.30:0.24

TABLE 2 Example 1 Example 2 Example 3 Example 4 Production Li/Me ratio —1.02 1.02 1.02 1.02 condition Maximum attained ° C. 900 900 900 900temperature Positive electrode active material Composition —Li_(1.02)Ni_(0.46)Co_(0.30)Mn_(0.24)O₂ Volume-average μm 7.9 9.0 9.8 7.0particle diameter MV (D90-D10)/average — 0.80 0.88 0.92 0.68 particlediameter MV Tapped density g/cc 2.61 2.70 2.68 2.49 Sparse density %2.45 2.61 2.63 2.70 Particle strength MPa 86 81 80 92 Primary ParticleLong diameter nm 930 701 992 623 Short diameter nm 369 332 386 312Aspect — 2.7 2.1 2.6 2.0 ratio (long diameter/short diameter) Crosssection — Radial structure structure Battery characteristics DischargingmAh/g 169.1 168.2 167.0 169.8 capacity Efficiency % 91.1 91.0 90.2 91.4Resistance Ω 1.84 1.95 2.08 1.76 Capacity retention % 78.9 78.5 78.280.2 rate@ after 500 cycles Compara. Compara. Compara. Compara. Compara.Example 1 Example 2 Example 3 Example 4 Example 5 Production Li/Me ratio— 1.02 1.02 1.02 1.02 1.02 condition Maximum attained ° C. 900 900 900900 900 temperature Positive electrode Composition —Li_(1.02)Ni_(0.46)Co_(0.30)Mn_(0.24)O₂ *1) *2) active materialVolume-average μm 5.1 7.9 4.4 12.0 6.7 particle diameter MV(D90-D10)/average — 0.50 0.66 0.54 1.00 0.64 particle diameter MV Tappeddensity g/cc 1.82 2.31 2.06 2.71 2.37 Sparse density % 35.40 0.60 0.610.20 0.24 Particle strength MPa 60 112 124 105 102 Primary Particle Longdiameter nm 1501 553 464 853 510 Short diameter nm 356 414 384 455 381Aspect — 4.2 1.3 1.2 1.9 1.3 ratio (long diameter/short diameter) Crosssection — Porous Random flocculation structure structure structureBattery Discharging mAh/g 168.5 162.3 165.3 160.4 162.5 characteristicscapacity Efficiency % 90.3 88.0 87.3 87.4 83.0 Resistance Ω 2.01 2.152.30 2.34 2.11 Capacity retention % 76.2 75.0 72.1 71.2 74.8 rate@ after500 cycles *1) Li_(1.02)Ni_(0.44)Co_(0.31)Mn_(0.25)O₂ *2)Li_(1.02)Ni_(0.46)Co_(0.30)Mn_(0.24)O₂

(Evaluation)

In the composite hydroxides of Examples, all of the values, namely, thevolume-average particle diameter MV, the [(D90−D10)/average particlediameter] that is the indicator representing a spread of the particlesize distribution, the ratio I(101)/I(001) of the diffraction peakintensity of the 101 plane (I(101)) to the peak intensity of the 001plane (I(001)) measured by the X-ray diffraction measurement, and thepore size, were within suitable respective ranges. In addition, thesecondary particles having the structure in which the primary particleshaving the aspect ratio of at least 3 were radially disposed (radialstructure) were formed. The composite hydroxides like these are the mostsuitable particles to obtain the positive electrode active materialhaving a high capacity and a long life, so that they can be suitablyused as the precursors of the positive electrode active material.

In addition, all the positive electrode active materials obtained inExamples had high particle fillability; and the coin-type batteriesusing these positive electrode active materials had high initialdischarging capacities and efficiencies. In addition, the positiveelectrode active materials obtained in Examples had excellent cyclecharacteristics and low positive electrode resistances, so that thesecondary batteries having excellent characteristics were able to beobtained.

On the other hand in Comparative Example 1, because the dissolved oxygenconcentration of the aqueous reaction solution in the crystallizationprocess was made high, oxidation of metals (especially manganese) tookplace in the obtained composite hydroxide, so that the secondaryparticle had a porous structure inside thereof. Because of this, thepore size thereof became large. In addition, the volume-average particlediameter MV was small and the particle fillability was poor. In thepositive electrode active material obtained in Comparative Example 1,because of the porous structure, the contact interface with theelectrolyte solution was large and the capacity was high, but because ofa low tap density, the volume energy density was low.

In Comparative Example 2, the nickel concentration of the aqueousreaction solution in the crystallization process was made low and theresidence time of the mixed aqueous solution was made long, so that inthe composite hydroxide obtained, the primary particle grew therebyleading to the structure in which the particles having almost the sameaspect ratio were flocculated (random flocculation structure) (FIGS.7(A) and 7(B)). Besides, the particles were so dense that they hardlyhad the pores having the size of up to 40 nm. In the positive electrodeactive material obtained in Comparative Example 2, the aspect ratios ofthe primary particles thereof were almost the same among themselves andthey had the structure in which the particles were seemingly flocculatedrandomly (FIG. 8(B)), so that the positive electrode resistance was highand the capacity was low. In addition, inside of the particle was sodense that it was easily cracked by the volume shrinkage upon chargingand discharging thereby resulting in a poor cycle characteristic.

In Comparative Example 3, the nickel concentration of the aqueousreaction solution in the crystallization process was made low so thatthe particles were not able to grow sufficiently well during the sameresidence time of the mixed aqueous solution as Example 1; as a result,the volume-average particle diameter MV in the composite hydroxidethereby obtained was small. Inside of the particle was dense, and it hadthe structure in which the primary particles having almost the sameaspect ratio were flocculated. In the positive electrode active materialobtained in Comparative Example 3, the volume-average particle diameterMV was so small that the tap density was low. For the same reasons asComparative Example 2, both the capacity and the life were poor.

In Comparative Example 4, the nickel concentration in the aqueousreaction solution in the crystallization process was made high so thatthe composition of the composite hydroxide thereby obtained shifted. Inaddition, in the obtained composite hydroxide, the primary particle grewthereby leading to the structure in which the primary particles havingalmost the same aspect ratio were flocculated. In the positive electrodeactive material obtained in Comparative Example 4, the aspect ratios ofthe primary particles were almost the same thereby leading to thestructure in which the particles are seemingly flocculated randomly withthe shifted composition. Therefore, the positive electrode resistancewas high and the capacity was low.

In Comparative Example 5, the temperature of the aqueous reactionsolution in the crystallization process was made high so that the insideof the particle of the obtained nickel-cobalt-manganese compositehydroxide was dense, and it had the structure in which the primaryparticles were randomly flocculated. In the positive electrode activematerial obtained in Comparative Example 5, inside of the particle wasdense with the structure in which the primary particles are seeminglyflocculated randomly, so that the capacity and the cycle characteristicwere poor.

Hereinafter, analysis results of the crystal orientation of the positiveelectrode active material of the present embodiment will be described.

Example 5 [Preparation of the Positive Electrode Active Material]

After the nickel-cobalt-manganese composite hydroxide obtained with thesame conditions as Example 1 each and lithium carbonate were weighed soas to give the Li/Me ratio of 1.04, they were fully mixed to obtain alithium mixture by using a shaker mixer (TURBULA Type T2C; manufacturedby Willy A. Bachofen AG (WAB)) with applying a strength that the shapeand structure of the precursor were able to be still retained (mixingprocess).

The lithium mixture thus obtained was inserted into a magnesia-madefiring vessel, and by using a sealed-type electric furnace, thetemperature thereof was raised in an air atmosphere with the flow ratethereof being 12 L/minute and with the temperature raising rate of 2.77°C./minute until 900° C., at which temperature the mixture was kept for10 hours; and then, it was cooled in the furnace to room temperature toobtain the lithium-transition metal composite oxide (firing process).

When the surface and cross section structures of thelithium-nickel-manganese oxide were observed with a scanning electronmicroscope, it was confirmed that similarly to the nickel-manganesecomposite hydroxide, the particle having good sphericity was obtained.The particle size distribution of the positive electrode active materialthus obtained was measured in the same way as the nickel-manganesecomposite hydroxide. It was confirmed that the volume-average particlediameter MV was 8.4 μm, and that [(D90−D10)/average particle diameter]was 0.80.

[Fabrication and Evaluation of the Battery]

For evaluation of the positive electrode active material thus obtained,the 2032 coin-type battery was used. As illustrated in FIG. 9(B), thecoin-type battery CBA2 is composed of the case CA and the electrode ELthat is accommodated in the case CA.

The case CA has the positive electrode can PC having a hollow structurewith one side thereof open and the negative electrode can NC that isdisposed in the open portion of the positive electrode can PC; and it isconfigured such that when the negative electrode can NC is disposed inthe open portion of the positive electrode can PC, the space may beformed in which the electrode EL is accommodated between the negativeelectrode can NC and the positive electrode can PC.

The electrode EL includes the positive electrode PE, the separator SE,and the negative electrode NE, and they are stacked in this order, inwhich they are accommodated in the case CA such that the positiveelectrode PE may contact with the inner surface of the positiveelectrode can PC and the negative electrode NE may contact with theinner surface of the negative electrode can NC.

The case CA is provided with the gasket GA; and with this gasket GA, thepositive electrode can PC and the negative electrode can NC are fixed inorder to keep an electrical insulation state therebetween. In addition,the gasket GA seals the space between the positive electrode can PC andthe negative electrode can NC, so that it also has the air-tight andliquid-tight functions between the inside and outside of the case CA.

This coin-type battery CBA2 was fabricated as follows. First, after 52.5mg of the obtained positive electrode active material, 15 mg ofacetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) weremixed, the resulting mixture was press molded with the applied pressureof 100 MPa to prepare the positive electrode PE having the diameter of11 mm and the thickness of 100 μm. The positive electrode PE thusprepared was dried at 120° C. in a vacuum dryer for 12 hours. Then, byusing this positive electrode PE, the negative electrode 3 b, theseparator SE, and the electrolyte solution, the coin-type battery CBA2was prepared under an Ar atmosphere in a globe box in which the dewpoint was controlled at −80° C.

For the negative electrode NE, a negative electrode sheet obtained bypunching out to a disk-like shape having the diameter of 14 mm was used,the sheet being the copper foil applied with graphite powders having theaverage particle diameter of about 20 μm and polyvinylidene fluoride.For the separator SE, a polyethylene porous film having the filmthickness of 25 μm was used. For the electrolyte solution, an equalamount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)(manufactured by Tomiyama Pure Chemical Industries, Ltd.) including 1 MLiClO₄ as the supporting electrolyte was used.

[Battery Evaluation]

The initial discharging capacity that was used to evaluate theperformance of the obtained coin-type battery CBA2 was defined asfollows.

The initial discharging capacity was measured as follows. Namely, afterthe open circuit voltage (OCV) was stabilized by allowing to leave thecoin-type battery CBA2 for about 24 hours after it was prepared, it wascharged to the cut-off voltage of 4.3 V with the current density to thepositive electrode being 0.1 mA/cm², and after 1 hour of pause, it wasdischarged to the cut-off voltage of 3.0 V, and thereby the capacity atthis time was regarded as the initial discharging capacity. Measurementof the charging and discharging capacities was carried out by using amulti-channel voltage/electricity generator (R6741A; manufactured byAdvantest Corp.).

When battery evaluation was carried out with regard to the coin-typebattery having the positive electrode formed by using the positiveelectrode active material, the initial discharging capacity was 167.9mAh/g.

[Orientation Evaluation]

The initial discharging capacity, the cycle capacity retention rate, andthe positive electrode resistance, used to evaluate the orientation ofthe obtained active material secondary particle in the radial directionby EBSD (electron backscatter diffraction method), are defined asfollows. In view of keeping the conductivity of the target sample formeasurement, when the target sample was set inside the measurementapparatus, fixing to the target sample holder was made by using aconductive paste (colloidal carbon paste).

With regard to the measurement instrument, a scanning electronmicroscope (SEM) equipped with a computer capable of analyzing thecrystal direction (ULTRA 55; manufactured by Carl Zeiss GmbH) was used.The acceleration voltage of an electron beam irradiated to the targetsample was about 15 kV with the current amount of about 20 nA.

The orientation information in the x-axis and the y-axis was obtained inthe strip of 2.5 μm×12.5 μm in the area to measure the crystal directionin the cross section of the target sample (plane to be measured), inwhich the measurement was made at 250,000 points in total.

In order to easily take the picture of the electron beam scattered by acamera that is installed in the SEM apparatus (Kikuchi beam), the targetsample (more specifically the plane to be measured, i.e., the crosssection) was tilted about 70 degrees from a horizontal plane so as toirradiate the scattered electron beam to the camera.

The crystal direction of the material obtained by EBSD changes dependingon the direction of the standard axis chosen by the observer. Usually,the crystal direction distribution diagram is represented, as thestandard axis, by any axis of the orthogonal coordinate axes composed ofan x-axis, a y-axis, and a z-axis. Hereinafter, the crystal directiondistribution diagrams with the standard axis of x-axis, y-axis, andz-axis are respectively called IPF-X, IPF-Y, and IPF-Z. FIG. 4(A) andFIG. 4(B) are the schematic drawings that express the observer'sviewpoints corresponding to each crystal direction distribution diagram.As depicted in FIG. 4(B), when the observation cross section is regardedas the plane of the paper, IPF-X is the crystal direction in thehorizontal direction on this plane as the standard. IPF-Y is in theperpendicular direction on this plane as the standard. On the otherhand, IPF-Z is the crystal direction in the vertical direction of theobservation cross section as the standard.

In the case of the positive electrode material, it is considered thatthe crystal direction information obtained when the edge of the positiveelectrode material particle in which the lithium ion is transferred withthe electrolyte solution is observed from the particle surface and thecrystal direction information of the path in which the lithium ioninside the particle is de-inserted and that is in the radial directionfrom the center of the particle to the outside thereof are important.Therefore, when the orientation evaluation of the x-axis direction withregard to the radial direction of the particle was carried out, theanalysis results of the IPF-X corresponding to the crystal directionobserved from these directions were used; and similarly, the analysisresults of the IPF-Y were used for the orientation in the y-axisdirection.

The scattered electron beam (Kikuchi beam) was observed with a camera,and the data of the Kikuchi pattern observed with the camera were sentto a computer, and then, the Kikuchi pattern was analyzed to determinethe crystal direction. For each measurement point of the determinedcrystal direction data of the target sample, the coordinates (x and y)and the Euler angles (ϕ1, Φ, and ϕ2) that indicate the crystal directionwere obtained.

The measurement points having the values of the Euler angles that wereobtained by the sample evaluation were distributed to each crystaldirection as the zone axis in accordance with the following conditions.

-   -   <001> axis: ϕ1=0°±30°, Φ=0°±30°, ϕ2=0°±30°    -   <100> axis: ϕ1=0°±30°, Φ=90°±30°, ϕ2=60°±30°    -   <110> axis: ϕ1=0θ±30°, Φ=90°±30°, ϕ2=120°±30°

In accordance with the rule described above, each measurement point canbe determined as to in which crystal direction the point is included.

After the above distribution, the ratio of each crystal direction in theplane to be measured was calculated by the number of the measurementpoints distributed to the respective crystal directions. The resultsthereof are listed in Table 3.

When executing this process, the commercially available analysissoftware for EBSD (analysis software for EBSD: Project Manager-Tango,sold by Oxford Instruments, Inc.) was used.

Evaluation results of the orientation and the average particle diameterof the lithium-nickel-manganese positive electrode active materialobtained in this Example, as well as the evaluation results of thecoin-type battery produced by using this positive electrode activematerial are listed in Table 3. In addition, the same items of Examples6 to 7 and Comparative Examples 5 to 6 are listed in Table 3.

Example 6

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the average particle diameter D50 ofthe precursor hydroxide in the reaction vessel in the crystallizationprocess was made to 10.2 μm. The evaluation results of the positiveelectrode active material thus obtained are listed in Table 1.

Example 7

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the average particle diameter D50 ofthe precursor hydroxide in the reaction vessel in the crystallizationprocess was made to 10.7 μm, and that N₂ and Air amounts were controlledin such a way that the dissolved oxygen concentration in the aqueousreaction solution was 3.0 mg/L. The evaluation results of the positiveelectrode active material thus obtained are listed in Table 1.

Comparative Example 6

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the average particle diameter D50 ofthe precursor hydroxide in the reaction vessel in the crystallizationprocess was made to 8.2 μm, and that N₂ and Air amounts were controlledin such a way that the dissolved oxygen concentration in the aqueousreaction solution was 0.2 mg/L. The evaluation results of the positiveelectrode active material thus obtained are listed in Table 1.

Comparative Example 7

The positive electrode active material was obtained and evaluated in thesame way as Example 1 except that the average particle diameter D50 ofthe precursor hydroxide in the reaction vessel in the crystallizationprocess was made to 10.1 μm, and that N₂ and Air amounts were controlledin such a way that the dissolved oxygen concentration in the aqueousreaction solution was 0.2 mg/L. The evaluation results of the positiveelectrode active material thus obtained are listed in Table 1.

TABLE 3 Average ab plane orientation particle (D90-D10)/average rate [%]diameter particle x-axis y-axis Charging Discharging MV[μm] diameter MVdirection direction Orientation capacity [mAh/g] capacity [mAh/g]Example 5 8.4 0.8 67.3 88.4 ◯ 184.3 167.9 Example 6 10.2 0.99 58.8 66.1◯ 182.5 167.8 Example 7 10.7 0.84 81.8 73.1 ◯ 183 167.4 Compara. Example6 8.2 0.66 84.7 34.6 X 185.8 164.5 Compara. Example 7 10.1 0.99 38.744.7 X 181.9 165.7

(Evaluation Results)

In the EBSD-based orientation evaluation of the positive electrodeactive materials of Examples, regarding orientations in the radialdirection of both the x-axis and y-axis, the rates of the ab plane,which is advantageous in insertion and de-insertion of Li ions, was atleast 55%. The positive electrode active materials of Examples exhibitedhigher discharging capacities as compared with the positive electrodeactive materials of Comparative Examples in which the rates of the abplane were less than 55%; and thus, it can be said that these particlesare suitable to obtain the positive electrode active material having ahigh capacity and a long life. In addition, the positive electrodeactive materials of Examples had a high fillability so that thecoin-type batteries using these positive electrode active materials werelow in the positive electrode resistance and high in the initialdischarging capacity and the efficiency; and thus, they are thebatteries having excellent characteristics.

On the other hand, in the nickel-cobalt-manganese composite hydroxideobtained in Comparative Example 6, because the dissolved oxygenconcentration in the solution of the crystallization reaction vessel wasmade low, oxidation of the transition metals, especially oxidation ofmanganese, was sluggish. Because of this, inside of the secondaryparticle became so sparse that orientation of the plate-like primaryparticles that constitute the precursor hydroxide were not able to havethe preferable morphology. The positive electrode active material ofComparative Example 1 synthesized from this nickel-cobalt-manganesecomposite hydroxide had a high resistance and a low capacity. Thedetails of the reason for this is not clear yet; but it is presumed thatbecause orientation in the radial direction of the primary particlesthat constitute the positive electrode active material was notsufficient so that diffusion of the Li ion was not facilitated therebyleading to a lower discharging capacity as compared with the positiveelectrode active materials of Examples.

Comparative Example 7 is the positive electrode active material obtainedby using the same method as Example 1 except that the precursor havingthe particle diameter made larger was used during the crystallizationprocess. Similarly to Comparative Example 6, in the positive electrodeactive material of Comparative Example 7, orientation of the plate-likeprimary particles that similarly constitute the precursor hydroxide werenot have the preferable morphology. In addition, the positive electrodeactive material of Comparative Example 7 had a high resistance and a lowcapacity. The details of the reason for this is not clear yet; but it ispresumed that because orientation in the radial direction of the primaryparticles of the positive electrode active material was not sufficientso that diffusion of the Li ion was not facilitated thereby leading to alower discharging capacity as compared with the positive electrodeactive materials of Examples.

Japanese Patent Application No. 2016-150620 as well as all theliterature cited in this specification are herein incorporated byreference in their entirety to the extent allowed by law.

DESCRIPTION OF REFERENCE SIGNS

-   -   1 Nickel-manganese composite hydroxide    -   2 Primary particle (nickel-manganese composite hydroxide)    -   3 Secondary particle (nickel-manganese composite hydroxide)    -   4 Void (nickel-manganese composite hydroxide)    -   C1 Central portion (nickel-manganese composite hydroxide)    -   d1 Particle diameter (nickel-manganese composite hydroxide)    -   L Direction of long diameter of primary particle    -   R1 Radial direction    -   R2 Area within 50% of a radius of the secondary particle from        the outer circumference toward the particle center    -   10 Positive electrode active material    -   12 Primary particle (positive electrode active material)    -   13 Secondary particle (positive electrode active material)    -   14 Void (positive electrode active material)    -   C2 Central portion (positive electrode active material)    -   d2 Particle diameter (positive electrode active material)    -   CBA1, CBA2 Coin-type battery    -   PE Positive electrode (electrode for evaluation)    -   NE Negative electrode    -   SE Separator    -   GA Gasket    -   WW Wave washer    -   PC Positive electrode can    -   NC Negative electrode can

1. A nickel-manganese composite hydroxide represented by General Formula(1): Ni_(x)Mn_(y)M_(z)(OH)_(2+α) (in Formula (1), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and x, y, z, and α satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8,x+y+z=1.0, and 0≤α≤0.4) and containing a secondary particle formed of aplurality of flocculated primary particles, wherein the primaryparticles have an aspect ratio of at least 3, and at least some of theprimary particles are disposed radially in a direction from a centralpart of the secondary particle to an outer circumference thereof, andthe secondary particle has a ratio (I(101)/I(001)) of a diffraction peakintensity I(101) of a 101 plane to a diffraction peak intensity I(001)of a 001 plane, measured by an X-ray diffraction measurement, of up to0.15.
 2. The nickel-manganese composite hydroxide according to claim 1,wherein in an area within 50% of a radius of the secondary particle fromthe outer circumference of the secondary particle toward the centralpart thereof, at least 50% of the primary particles in number relativeto a total number of the primary particles present within this area aredisposed radially.
 3. The nickel-manganese composite hydroxide accordingto claim 1, wherein a total pore volume in a pore volume distribution isat least 0.015 cm³/g and up to 0.03 cm³/g.
 4. The nickel-manganesecomposite hydroxide according to claim 1, wherein a volume-averageparticle diameter MV is at least 5 μm and up to 20 μm, and[(D90−D10)/average particle diameter] that is an indicator to representa spread of particle size distribution is at least 0.7.
 5. A method forproducing a nickel-manganese composite hydroxide represented by GeneralFormula (1): Ni_(x)Mn_(y)M_(z)(OH)_(2+α) (in Formula (1), M is at leastone additional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf Ta,Fe, and W; and x, y, z, and α satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8,x+y+z=1.0, and 0≤α≤0.4) and containing a secondary particle formed of aplurality of flocculated primary particles, the method comprising acrystallization process of forming a nickel-manganese compositehydroxide by neutralizing a salt containing at least nickel and a saltcontaining at least manganese in an aqueous reaction solution, whereinin the crystallization process, a dissolved nickel concentration in theaqueous reaction solution is controlled in a range of at least 300 mg/Land up to 1,500 mg/L, a dissolved oxygen concentration is controlled ina range of at least 0.5 mg/L and up to 3.5 mg/L, and a stirring powerapplied to the aqueous reaction solution is controlled in a range of atleast 4 kW/m³ and up to 8 kW/m³.
 6. The method for producing anickel-manganese composite hydroxide according to claim 5, wherein thecrystallization process includes continuously adding a mixed aqueoussolution including nickel and manganese into a reaction vessel andoverflowing slurry including nickel-manganese composite hydroxideparticles formed by neutralization to recover the particles.
 7. Themethod for producing a nickel-manganese composite hydroxide according toclaim 6, wherein in the crystallization process, a residence time of themixed aqueous solution in the reaction vessel is at least 3 hours and upto 15 hours.
 8. A method for producing a positive electrode activematerial for a nonaqueous electrolyte secondary battery, the methodcomprising: a process of mixing the nickel-manganese composite hydroxideaccording to claim 1 and a lithium compound to obtain a mixture; and aprocess of firing the mixture to obtain a lithium-nickel-manganesecomposite oxide.
 9. The method for producing a positive electrode activematerial for a nonaqueous electrolyte secondary battery according toclaim 8, wherein the nickel-manganese composite hydroxide is obtained bythe method comprising a crystallization Process of forming anickel-manganese composite hydroxide by neutralizing a salt containingat least nickel and a salt containing at least manganese in an aqueousreaction solution, Wherein, in the crystallization process, a dissolvednickel concentration in the aqueous reaction solution is controlled in arange of at least 300 me/L and up to 1,500 mg/L, a dissolved oxygenconcentration is controlled in a range of at least 0.5 m/L and up to 3.5mg/L, and a stirring power applied to the aqueous reaction solution iscontrolled in a range of at least 4 kW/m³ and up to 8 kW/m³.
 10. Apositive electrode active material for a nonaqueous electrolytesecondary battery, the positive electrode active material comprising: alithium-nickel-manganese composite oxide containing a secondary particleformed of a plurality of flocculated primary particles and representedby General Formula (2): Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(Z+β) (in Formula(2), M is at least one additional element selected from Co, Ti, V, Cr,Zr, Nb, Mo, Hf, Ta, Fe, and W; and u, x, y, z, and β satisfy−0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5),wherein when an arbitrary radial direction from a center of a crosssection of the secondary particle toward an outside thereof is regardedas an x-axis direction and a direction perpendicular to the x-axisdirection is regarded as a y-axis direction, an orientation rate of acrystal ab plane measured by an electron backscatter diffraction methodis at least 55% in each of the x-axis direction and the y-axisdirection.
 11. A positive electrode active material for a nonaqueouselectrolyte secondary battery, the positive electrode active materialcomprising: a lithium-nickel-manganese composite oxide containing asecondary particle formed of a plurality of flocculated primaryparticles and represented by General Formula (2):Li_(1+u)Ni_(x)Mn_(y)M_(z)O_(2−β) (in Formula (2), M is at least oneadditional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe,and W; and u, x, y, z, and β satisfy −0.05≤u≤0.5, 0.1≤x≤0.8, 0.1≤y≤0.6,0≤z≤0.8, x+y+z=1.0, and 0≤β≤0.5), wherein the primary particles have anaspect ratio of at least 2, and at least some of the primary particlesare disposed radially in a direction from a central part of the particleto an outer circumference thereof, a sparse density obtained from animage analysis result of a SEM image of a cross section of the secondaryparticle is at least 0.5% and up to 25%, and a particle strength is atleast 70 MPa and up to 100 MPa.
 12. The positive electrode activematerial for a nonaqueous electrolyte secondary battery according toclaim 11, wherein in an area within 50% of a radius of the secondaryparticle from the outer circumference of the secondary particle towardthe central part thereof, at least 50% of the primary particles innumber relative to a total number of the primary particles presentwithin this area are disposed radially.
 13. The positive electrodeactive material for a nonaqueous electrolyte secondary battery accordingto claim 10, wherein a volume-average particle diameter MV is at least 5μm and up to 20 μm, and [(D90−D10)/average particle diameter] that is anindicator to represent a spread of particle size distribution is atleast 0.7.
 14. A nonaqueous electrolyte secondary battery comprising: apositive electrode that comprises the positive electrode active materialfor a nonaqueous electrolyte secondary battery according to claim 10.